the only one i would even consider buying over corsair would be a PC P&C...and then it would have to be one heck of a deal. i probably wouldnt switch even then.
On my 450vx I run my sli 8800gt rig, 2GB RAM, 5000+ BE, barricuda 7.1, dual 500gb HDD...no issues at all. I like the corsairs, 4 systems in the house and all have corsair psus now. I have a gamerxstreme but sold it for the 550.