I can not confirm. I'm uploading with 2 different vps from the Netherlands with a total of 200mb/second. But the upload per file is mostly between 8-15mb/sec. I have raised the maximum data transfer. A testdowload of a larger file gave 170-190mb/sec. In a conversation with the support I was told that the maximum API calls may be exceeded at the beginning, only when longer exceed Box then reports to a personal. But no access will be restricted if the limit is exceeded. Also, the API limit can be increased permanently for a surcharge. Rclone chunk with 49Gi works perfectly for me.