I used the gx-450 on system i just sold.
My old i7 2600k, Asus P8P67Pro, 8gb, AMD 6770, 1tb 7200 rpm drive, 60gb Ocz SSD.
System runs fine at 4.4ghz, but I clocked it down to stock speeds since I used the stock cooler.
Seems a lot of people over buy a psu, buying waaaaay more psu than they will ever use.
I'm still rocking an Antec 650 with my setup, and I had more things in my pc's than the average person.
Q6600 @ 3Ghz, 8gb ddr2, gtx285, 9600gt, bluray/hd-DVD/DVD-rw, 9 7200rpm drives, 3 90mm fans, 1 120mm fan
With my 3 monitors, 2 large powered speakers, 2 network switches, and some other items, I would pull 390watts from the wall with the CPU and gpu at 100% load. That means the psu is using only 310watts on the dc side, so I've got 340watts of headroom.
My current setup only has 6 hard drives and 2 SSD's, a bluray/hd-DVD/DVD-rw, i7 3770k @ 4.4ghz, corsair h60 with 2 120mm fans, 3 240mm case fans, hd5850 video card. I have a 3.5" hot swap bay so I'll sometimes have 7 hard drives in the machine. http://transamws6.com/pics/pc/2010/3770k.jpg