I run a mkii crb as my primary weapon.
I too thought the same as you regarding upgrading straight away, but several months down the road and a lot of use, I can categorically say that I really wouldn't bother.
I stuck in a Prometheus 6.03 barrel, maple leaf bucking/nub, from there on I experienced a serious drop in fps, averaging 275. Don't get me wrong, it was accurate and had reasonable range, but upon putting the stock barrel,bucking/nub back in and putting a wrap of PTFE around the bucking, it now happily sits around 340.
All I've now done is change out the stock spring to an m100,and clip half a coil off.
From playing on Saturday I'm extremely happy with it's performance now.
Stick an 11.1 in it and away you go.