I did some testing today with seekspeed using ncw tool https://github.com/ncw/rclone/blob/master/cmd/mount/test/seek_speed.go
MOUNTS
unionfs-fuse -o cow,allow_other,nonempty,auto_cache,sync_read /storage/local=RW:/mnt/flixlocal=RO:/mnt/dropboxcrypt=RO /mnt/cloud
rclone mount dropboxcrypt: /mnt/dropboxcrypt --allow-other --default-permissions --read-only --dir-cache-time 1m --max-read-ahead 1M --buffer-size 512M --fast-list --log-level ERROR --log-file=/home/plex/logs/mountdropboxcrypt.log
rclone mount gdrivecrypt: /mnt/gdrivecrypt --allow-other --default-permissions --read-only --dir-cache-time 1m --max-read-ahead 1M --buffer-size 512M --fast-list --log-level ERROR --log-file=/home/
$ go run seekspeed.go "/mnt/cloud/series/You/Season 01/You - S01E02 - WEBDL-1080p.mkv"
2019/02/02 08:21:19 Reading 170511 from 604055314
2019/02/02 08:21:22 Reading 459963 from 561434709
2019/02/02 08:21:24 Reading 643462 from 753379961
2019/02/02 08:21:26 Reading 578220 from 270696830
2019/02/02 08:21:29 Reading 280484 from 167837760
2019/02/02 08:21:30 Reading 350895 from 305691948
2019/02/02 08:21:32 Reading 614385 from 709112814
2019/02/02 08:21:34 Reading 300314 from 144299763
2019/02/02 08:21:36 Reading 285845 from 648782408
2019/02/02 08:21:37 Reading 625634 from 126962086
2019/02/02 08:21:39 Reading 67802 from 92409449
2019/02/02 08:21:40 Reading 401042 from 863126279
2019/02/02 08:21:42 Reading 445739 from 858636914
2019/02/02 08:21:43 Reading 85240 from 300820544
2019/02/02 08:21:45 Reading 923639 from 698649260
2019/02/02 08:21:47 Reading 1011576 from 559295272
2019/02/02 08:21:49 Reading 686863 from 842940711
2019/02/02 08:21:51 Reading 756044 from 225453075
2019/02/02 08:21:53 Reading 82935 from 382800547
2019/02/02 08:21:55 Reading 543634 from 828441564
2019/02/02 08:21:57 Reading 180882 from 753902051
2019/02/02 08:21:59 Reading 402243 from 89020412
2019/02/02 08:22:00 Reading 670611 from 905922076
2019/02/02 08:22:02 Reading 735972 from 383986151
2019/02/02 08:22:04 Reading 1025113 from 977907806
2019/02/02 08:22:06 That took 46.701144257s for 25 iterations, 1.86804577s per iteration
$ go run seekspeed.go "/mnt/dropboxcrypt/series/You/Season 01/You - S01E02 - WEBDL-1080p.mkv"
2019/02/02 08:23:48 Reading 170511 from 604055314
2019/02/02 08:23:52 Reading 459963 from 561434709
2019/02/02 08:23:54 Reading 643462 from 753379961
2019/02/02 08:23:56 Reading 578220 from 270696830
2019/02/02 08:23:57 Reading 280484 from 167837760
2019/02/02 08:23:59 Reading 350895 from 305691948
2019/02/02 08:24:01 Reading 614385 from 709112814
2019/02/02 08:24:02 Reading 300314 from 144299763
2019/02/02 08:24:05 Reading 285845 from 648782408
2019/02/02 08:24:06 Reading 625634 from 126962086
2019/02/02 08:24:08 Reading 67802 from 92409449
2019/02/02 08:24:10 Reading 401042 from 863126279
2019/02/02 08:24:11 Reading 445739 from 858636914
2019/02/02 08:24:14 Reading 85240 from 300820544
2019/02/02 08:24:16 Reading 923639 from 698649260
2019/02/02 08:24:19 Reading 1011576 from 559295272
2019/02/02 08:24:20 Reading 686863 from 842940711
2019/02/02 08:24:21 Reading 756044 from 225453075
2019/02/02 08:24:23 Reading 82935 from 382800547
2019/02/02 08:24:25 Reading 543634 from 828441564
2019/02/02 08:24:27 Reading 180882 from 753902051
2019/02/02 08:24:29 Reading 402243 from 89020412
2019/02/02 08:24:30 Reading 670611 from 905922076
2019/02/02 08:24:32 Reading 735972 from 383986151
2019/02/02 08:24:35 Reading 1025113 from 977907806
2019/02/02 08:24:37 That took 48.515593192s for 25 iterations, 1.940623727s per iteration
go run seekspeed.go "/mnt/gdrivecrypt/series/You/Season 01/You - S01E02 - WEBDL-1080p.mkv"
2019/02/02 08:32:58 Reading 170511 from 604055314
2019/02/02 08:33:09 Reading 459963 from 561434709
2019/02/02 08:33:17 Reading 643462 from 753379961
2019/02/02 08:33:17 Reading 578220 from 270696830
2019/02/02 08:33:18 Reading 280484 from 167837760
2019/02/02 08:33:19 Reading 350895 from 305691948
2019/02/02 08:33:20 Reading 614385 from 709112814
2019/02/02 08:33:20 Reading 300314 from 144299763
2019/02/02 08:33:21 Reading 285845 from 648782408
2019/02/02 08:33:30 Reading 625634 from 126962086
2019/02/02 08:33:39 Reading 67802 from 92409449
2019/02/02 08:33:39 Reading 401042 from 863126279
2019/02/02 08:33:40 Reading 445739 from 858636914
2019/02/02 08:33:49 Reading 85240 from 300820544
2019/02/02 08:33:57 Reading 923639 from 698649260
2019/02/02 08:33:58 Reading 1011576 from 559295272
2019/02/02 08:33:59 Reading 686863 from 842940711
2019/02/02 08:33:59 Reading 756044 from 225453075
2019/02/02 08:34:00 Reading 82935 from 382800547
2019/02/02 08:34:01 Reading 543634 from 828441564
2019/02/02 08:34:10 Reading 180882 from 753902051
2019/02/02 08:35:07 Reading 402243 from 89020412
2019/02/02 08:35:38 Reading 670611 from 905922076
2019/02/02 08:35:41 Reading 735972 from 383986151
2019/02/02 08:35:41 Reading 1025113 from 977907806
2019/02/02 08:35:47 That took 2m48.138221841s for 25 iterations, 6.725528873s per iteration
Added vfs fags to gdrivecrypt
rclone mount gdrivecrypt: /mnt/gdrivecrypt --allow-other --default-permissions --read-only --dir-cache-time 1m --max-read-ahead 1M --buffer-size 512M --fast-list --vfs-read-chunk-size 128M --vfs-read-chunk-size-limit off --log-level ERROR --log-file=/home/plex/logs/mountgdrivecrypt.log
go run seekspeed.go "/mnt/gdrivecrypt/series/You/Season 01/You - S01E02 - WEBDL-1080p.mkv"
2019/02/02 08:37:50 Reading 170511 from 604055314
2019/02/02 08:37:51 Reading 459963 from 561434709
2019/02/02 08:37:52 Reading 643462 from 753379961
2019/02/02 08:38:00 Reading 578220 from 270696830
2019/02/02 08:38:09 Reading 280484 from 167837760
2019/02/02 08:38:09 Reading 350895 from 305691948
2019/02/02 08:38:19 Reading 614385 from 709112814
2019/02/02 08:38:28 Reading 300314 from 144299763
2019/02/02 08:38:28 Reading 285845 from 648782408
2019/02/02 08:38:29 Reading 625634 from 126962086
2019/02/02 08:38:29 Reading 67802 from 92409449
2019/02/02 08:38:30 Reading 401042 from 863126279
2019/02/02 08:38:31 Reading 445739 from 858636914
2019/02/02 08:38:31 Reading 85240 from 300820544
2019/02/02 08:38:32 Reading 923639 from 698649260
2019/02/02 08:38:33 Reading 1011576 from 559295272
2019/02/02 08:38:38 Reading 686863 from 842940711
2019/02/02 08:38:46 Reading 756044 from 225453075
2019/02/02 08:38:59 Reading 82935 from 382800547
2019/02/02 08:39:08 Reading 543634 from 828441564
2019/02/02 08:39:08 Reading 180882 from 753902051
2019/02/02 08:39:09 Reading 402243 from 89020412
2019/02/02 08:39:09 Reading 670611 from 905922076
2019/02/02 08:39:10 Reading 735972 from 383986151
2019/02/02 08:39:11 Reading 1025113 from 977907806
2019/02/02 08:39:11 That took 1m21.143056168s for 25 iterations, 3.245722246s per iteration
Added vfs fags to dropboxcrypt
rclone mount dropboxcrypt: /mnt/dropboxcrypt --allow-other --default-permissions --read-only --dir-cache-time 1m --max-read-ahead 1M --buffer-size 512M --fast-list --vfs-read-chunk-size 128M --vfs-read-chunk-size-limit off --log-level ERROR --log-file=/home/plex/logs/mountdropboxcrypt.log
go run seekspeed.go "/mnt/dropboxcrypt/series/You/Season 01/You - S01E02 - WEBDL-1080p.mkv"
2019/02/02 08:47:15 Reading 170511 from 604055314
2019/02/02 08:47:18 Reading 459963 from 561434709
2019/02/02 08:47:20 Reading 643462 from 753379961
2019/02/02 08:47:22 Reading 578220 from 270696830
2019/02/02 08:47:24 Reading 280484 from 167837760
2019/02/02 08:47:25 Reading 350895 from 305691948
2019/02/02 08:47:27 Reading 614385 from 709112814
2019/02/02 08:47:29 Reading 300314 from 144299763
2019/02/02 08:47:30 Reading 285845 from 648782408
2019/02/02 08:47:32 Reading 625634 from 126962086
2019/02/02 08:47:34 Reading 67802 from 92409449
2019/02/02 08:47:35 Reading 401042 from 863126279
2019/02/02 08:47:37 Reading 445739 from 858636914
2019/02/02 08:47:40 Reading 85240 from 300820544
2019/02/02 08:47:41 Reading 923639 from 698649260
2019/02/02 08:47:42 Reading 1011576 from 559295272
2019/02/02 08:47:44 Reading 686863 from 842940711
2019/02/02 08:47:47 Reading 756044 from 225453075
2019/02/02 08:47:48 Reading 82935 from 382800547
2019/02/02 08:47:50 Reading 543634 from 828441564
2019/02/02 08:47:51 Reading 180882 from 753902051
2019/02/02 08:47:53 Reading 402243 from 89020412
2019/02/02 08:47:54 Reading 670611 from 905922076
2019/02/02 08:47:56 Reading 735972 from 383986151
2019/02/02 08:48:01 Reading 1025113 from 977907806
2019/02/02 08:48:04 That took 48.730219968s for 25 iterations, 1.949208798s per iteration
RESULT
Dropbox without vfs: That took 48.515593192s for 25 iterations, 1.940623727s per iteration
Dropbox with vfs: That took 48.730219968s for 25 iterations, 1.949208798s per iteration
Gdrivrcrypt wihtout vfs: That took 2m48.138221841s for 25 iterations, 6.725528873s per iteration
Gdrivecrypt with vfs: That took 1m21.143056168s for 25 iterations, 3.245722246s per iteration