Go for the 450 as the big boy has some interesting fueling issues which nobody has managed to cure. My dads mate got one and when racing it doesn't have a problem but on the road its a pile of steaming poo. As an ex motarder i've spoken with a few guys who race and all recon the 450's dam near as fast and far more useable plus its cheaper.
Sexy looking thing though....... If only the wife would let me race again, mmmmmm.