The only critique of your system I have is that instead of 1 single 1TB harddrive, I would have put 2x500Gb drives in a RAID 0(i think) striped configuration to nearly double the harddrive bandwidth. It makes the computer seem nearly twice as fast, because it actually is twice as fast!
Also x64 has nothing you need to worry about. I've been on it for nearly 2 years and I've had no compatibility problems with any software made past 2001. Enjoy all that 4Gb of memory to the fullest.
P.S.: Your rig is faster than most people on this forum so don't try to be all humble about it's performance! Two GTX's is insane, however I would suggest sending them back for two G92 GTS's for the extra video processing features