Corsair Professional Series Gold AX1200

It is a good and efficient PSU and at a good price for a 1200watt if you need that much! (There are many more good and efficient PSU's)

Any chance you could tell me some? - My system runs at a 550-600 watts full load.

And if I'm not mistaken I've heard that PSU's work best at 50% load.

This one would be plenty for you then http://www.newegg.com/Product/Product.aspx?Item=N82E168...
PSU's have the best efficiency at 50-80% load http://www.corsair.com/power-supplies/modular-psus/prof...
Even the 750 would be enough.

PSU's generally hit their best efficiency point at 50% load. It tails off slowly in each direction. But at your load, I'd get an 850 watter.

For comparison purposes , the list below contains performance ratings (10 scale) at jonnyguru.com / prices as per newegg on 12/31/2010 and ones w/ double asterisks (**) made it onto silentpcreview.com's Editor's Choice List meaning they excelled at both electronic and acoustic performance:


Antec SG-850 - 10.0 ($250) **
Antec CP-850 - 10.0 ($120) **
XFX 850W Black Edition 10.0 ($110)
Corsair HX850 850W - 10.0 ($170)

Antec TruePower Quattro (TPQ-850) - 9.5 ($150)
Corsair TX850 - 9.5 ($130)
Seasonic M12D 850W - 9.5 (NLA) **
NorthQ Giant Connector 850W - 9.5 (NFS)
Etasis ET850 - 9.5 (NLA)
Silverstone Zeus ST85ZF - 9.5 (NLA)

Enermax Revolution 85+ 850W - 9.0 (OOS)

Thrmaltake Toughpower XT 850W - 8.5 (NLA)
OCZ Z Series 850W - 8.5 ($165)

NorthQ Black Magic Flex 850W - 8.0 (NFS)
Coolmax CTG-850 - 8.0 (NFS)

SilverStone Decathlon DA850 - 7.5 (NLA)
Enermax Galaxy DXX 850W EGX850EWL - 7.5 (NFS)

SilverStone Strider ST85F - 7.0

Silverstone Element ST85EF 850W - 6.0


OOS - Out of Stock / NFS - Not For Sale / NLA = No Longer Available

Given today's pricing, unless you have a compatible Antec case, I'd say the XFX Black is a "no brainer".

http://www.newegg.com/Product/Product.aspx?Item=N82E168...