Drive-train shaft size

[Andrew Schuetze]

I did a search but didn't see what I am looking for at first glance.
I just recieved some samples from IGUS that are plastic bearings and such. Their website lists two FIRST teams who used them or other products in the last two years.

My question is two fold:

1. What size of shaft do you use on your drive-train if it is a roller chain sprocket type? We have a lot of stock in 5/8 with a keyway since the SkyWay Beadlock wheels have that bore type. I am not an ME so I don't feel solid on doing calculations but that seems to be extra beefy for FIRST class robots. Is 3/8 or 7/16 too weak?

2. If a robot only competes in one regional and then the championships, would the IGUS plastic bearings hold up to the abuse? Pillow block sets of steel are a big weight user. We are not at a fabrication level to be able to use flanged bearing set into the frame.