What should i take ?

[Dreadfull]

Hi, i wanna buy a Thermaltake PSU (i'm a fan) but i don't know how "big" it should be

It should keep these up:

2 x Intel Xeon Quad-Core 2,5 GHz
16 GB DDR2 (8x2GB) - Kingston ValueRAM ECC Fully Buffered
3 WD VelociRaptor hdd's
1 DVD-RW
ASUS MB (DSBF-DE, onboard video/audio/lan)

I was thinking of Thermaltake W0163RE Toughpower QFan 650W, is it ok ? (my problem is i don't know how much the RAM needs)

Thanks!