There is a guy on eBay who has 32 through 40 tooth bolt-on chainrings for the M620 spline: https://www.ebay.com/itm/134032797529?I’m going to a 36 tooth, have one at home already just waiting on my adapter to mount it up. I’m thinking it will only help it, it would be much less rotating mass so easier on the motor and gearing down will be ok as it’s already faster than I’ll need most of the time
My main concern with going lower is the added torque on the larger rear gears -- the top 3 are reportedly weaker due to the relatively large weight reducing cutouts compared to the smaller ones. I figure 40 should be okay, and maybe 38, but 32 may be taking it too far, past the last straw sort of thing?