As long as you have the a/p on when you are level in RVSM airspace there should not be any issue with handflying it up to cruise. Your RVSM checks (I know you do 'em and write them down on the flightplan, right?) are done in level flight. Clearance to climb to and maintain an altitude gives you all that airspace up to that altitude.

I like to handfly. The 757 flys real nice and I've even done a few PHX to SAN and PHX to LAS (both always at FL 280) legs without using the a/p at all. F/Os get a kick out of it. I am back on the Airbus right now and I've done one LAS to LAX leg at 260 without the a/p, it was not nearly as much fun. I always handfly IFR approaches unless it is CAT 2 or a non precision (managed NAV) to minimums. Company wants us to use automation as much as we can but I see too many weak pilots that just click it on at 200' and off at 500'. They wonder why they struggle in the sim.