Is a 750W Corsair enough for this?

well, it is plenty if you plan to use a radeon 5870 or less.

What he said, if you go for a SLI Fermi I would suggest something like this http://www.jonnyguru.com/modules.php?name=NDReviews&op=...

yeah

but cm psus suck don they?

Yeah but if you want to add a 2 Fermis no instead you could get this if you want Fermis:
http://www.jonnyguru.com/modules.php?name=NDReviews&op=...
If you add a 5XXX your good.

It got a 8.5 from Johny Guru.

A quality 750W PSU can handle even a 5970, a GTX480 or a 5850CF.

Here you have some good options:

ANTEC TRUEPOWER NEW 750W (by Seasonic)
CORSAIR HX750 750W (by CWT)
Enermax MODU87+ 700W
SEASONIC M12D 750W
SEASONIC X-750 750W
THERMALTAKE Toughpower XT 775W (by CWT)
XFX Black Edition 750W (by Seasonic)

For a 5870CF, a 5970CF or a GTX470SLI, I would go for a quality 850W PSU:

ANTEC Signature SG850 850W (by Delta Electronics)
CORSAIR HX850 850W (by CWT)
CORSAIR TX950 950W (by CWT) (no modular)
XFX BLACK EDITION 850W (by Seasonic)
ENERMAX Revolution85+ 850W
SEASONIC M12D 850W
THERMALTAKE Toughpower XT 875W (by CWT)

For a GTX480 SLI, I would go for a quality 1000W PSU:

CORSAIR HX1000 1000W (by CWT)
ANTEC Truepower Quattro 1200W (by Enhance Electronics)
ENERMAX Revolution85+ 1050W
ENERMAX Galaxy Evo 1250W
THERMALTAKE Toughpower Cable Management 1200W (W0133 model) (by CWT)
SAPPHIRE PurePSU 1250W (by Enermax)
IKONIK Vulcan 1200W (by CWT)

Corsair PSU calculator

http://www.corsair.com/

Antec PSU calculator

http://www.antec.outervision.com/

Antec corsair, seasonic are all good supply