You have to remember that with bearings they are designed to run for many thousands of hours. You need them to run for a max of 30 minutes (10 fights through robot wars at 3 minutes a piece) plus maybe 5 minutes for testing / tech check etc. Getting close to the max rpm wouldn't be a concern for me.

I wasn't aware that SPA pulleys came that small! May have to look at them again myself.

As far as the rpm limits etc I'd drop the guys at robochallenge an email and ask them what their thoughts on it are.