the corsair 400w peaks at 480w and has 30a on its 12v rail. your PC won't break 300w (probably wont break 250w) and needs 20a tops. both the athlon II and ATI 5770 are extremely efficient.
Core i7 Test System Specs
- Intel Core i7 965 Extreme Edition (Overclocked @ 3.70GHz)
- x3 2GB G.Skill DDR3 PC3-12800 (CAS 9-9-9-24)
- Asus P6T Deluxe (Intel X58)
- Seagate 500GB 7200-RPM (Serial ATA300)