Well actually i have a separate benching rig. You are probably looking at my main rig though.

But i will probably try out my main rig's cpu and gpu's in the benching rig eventually.
My cheap a$$ benching rig currently:
DFI UT P35 T2R - i plan to get alot of use out of this mobo. When i get some better chips, i plan on shooting for 600+ fsb.
2x1gb 1066 Dominators
Pentium D 915 and P4 660 - i have yet to try the 660. I am currently working on maxing the 915. I have hit 4.6ghz fairly stable on air right now with the 915.
ATI x600xt
Antec 550w psu
The x600xt, 550w psu, and p4 660 came from an old rig. The PD 915 i had laying around. The mobo i bought here, and the ram is from my main rig, which i replaced with 2x2gb 1066 Doms. (I had 4x1gb Doms originally)
I know this will never come near 750w. But if i use my main rig's cpu and gpu's i definitely will need more power than 550w. I also plan on picking up some more chips for benching (e5200, e7400, e3200). Another reason i want a new psu for my benching rig is that the current one is 4-5 years old now. I honestly don't know how much longer it will last.
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I actually have thought up a little plan, since i don't have the $ for a quality 1000w psu. What i am figuring is that i get a 750 or 850w psu now (probably the 750tx or 850tx.) Then, when i have the $ for really powerful hardware later, i could purchase a 1000w psu or something similar. So smaller now, and bigger later. Does this seem like a reasonable plan?