Perfect. Found those in the docs. But perhaps I spoke too soon. After 4 hours, the average speed has dropped to 7 kBytes a sec with over 3 weeks remaining. It uploaded about 100MB in the first couple of minutes and basically nothing in the remaining time.
So It's not erroring on Too many requests anymore, and nor does the log show throttled, but it would appear I'm still being limited in some capacity. I've since revised my command to include the following restrictions:
--tpslimit 5
--checkers 1
--transfers 1
--exclude .DS_Store
I've confirmed its not the network throttling, so I'm left to believe I'm just at the perils of Microsoft here. I've started a new copy operations and with those parameters it is behaving a bit better - done about 330M in 26 minutes.