It's the only way to get hold of C4/5 as it's extremely unlikely that it'll ever be hacked like SX3 was.
But it's a good DAW, been using C4 (and demo'd C5) a fair amount over the last year, mainly for 8.0 (circular speaker setup) audio projects, pretty stable (although C4 had bugs galore).
As for 64bit, double check that all of your VSTs/Plugins work as i had a few 32bit VSTs that didn't want to know even though C4/5 have this "vst bridge".
Greenlizard0 - Cubase 5 is around the £450 mark, whilst Cubase Studio 5 (slightly cut down, missing a few features) is about £300. Is a good bit of a kit but you can pick up a Protools setup for that price, be it an M-audio 2626 interface (offers so some of the best preamps for the price) and Protools M-powered.