Soz for the doublepost, but I thought I'd answer the question in the back of your mind (something that I was asking when 1st encountering the same problem with an upgrade).
MOST power supplies (very few exceptions like the Corsair ones), rate the power consumption over all the lines totalling up to the final wattage. This is not false in any way, just a bit misleading, since a lot of power (wattage) is wasted on the 5V and 3.3V lines. Some power supplies also have Dual-rail systems, while this was good in teh past, to power hard drives and components separately from gfx cards and what not, it doesnt hold true to todays standards as the GFX card power requirements have litterly exploded in the last few years. Most significantly, the dual-rail system fails because, while the total (combining both 12V rails) may result in 40Amps, the split of 20Amps per rail at what was previously a shocking efficiency rate (old PSU systems had ratings as low as 50% efficiency) result in an inadequate Amp rating even when combining the rails;
Above case in point, 2 X 12V rails with 20Amps each, combined to get 40Amps @ 50% efficiency = only actually getting 20Amps on the Combined rails - very bad.
Anyway, hope you kinda understand all this technical mumbo jumbo.
These days - SINGLE RAIL guys n girls, with MAX rating on the 12V rail.