From EVGA's site for the Superclocked version of the card:
Requirements
Minimum of a 400 Watt power supply.
(Minimum recommended power supply with +12 Volt current rating of 22 Amp Amps.)
Minimum 450 Watt for SLI mode system.
(Minimum recommended power supply with +12 Volt current rating of 24 Amp Amps.)
An available 6 pin PCI-E power connector (hard drive power dongle to PCI-E 6 pin adapter included with card)
In other words the 450 will be sufficient. However you may want to look at the OCZ GameXStream 600w unit. Same price after rebate.
Newegg.com - OCZ GameXStream OCZ600GXSSLI 600W ATX12V Power Supply 100 - 240 V CB/CE/CSA/UL/FCC - Power Supplies
I have been running a fairly heavily overclocked Opteron 170, 4Gb overclocked ram, and an EVGA 8800GT SSC for a year on the 700w model w/o any complaints or issues. Info about 9th post down on this thread
My proposed Computer
I have a 420w OCZ psu that I have been running a 4000+ cpu, 2Gb ram, and a 6800GT for about four years without any issue.
Corsair makes an solid PSU, but OCZ does as well. The OCZ 600w unit would be more likely to support higher drawing components in the future should you decide to upgrade down the road. With the 450w, you would probably have to replace it. The 600w OCZ has two PCI-E connectors to the single supported on the Corsair 450w.
Your call, nothing wrong with the 450w unit for this build.