PSU Amps per Rail and Overview of PSU Selection

Hello,

So I've got the following build set up (with an SSD and an external HDD that I occasionally use):

CPU: i5-2500k
Motherboard: ASRock Extreme3 Gen3
GPU: MSI Twin Frozr II OC 7850 OR Hawk 6870 (let's go with the 6870, since it uses more power. I'm still figuring out the budget)
RAM: 2x4GB G.Skill 1.5v 1600 CAS9
Case: Fractal R3
Cooler: Hyper 212 Evo

I've got one of the following PSUs lined up. I've heard mixed things about OCZ, as well. Here are the two:

OCZ
PC Power and Cooling 650W

Now, I was going to get the 750W PC Silencer MK II Silver Rated PSU, but it's non-modular (a slight problem with the Fractal R3 and me being a first time builder) and I honestly don't need 750W... I'm never going to Crossfire (or SLI). Overclocking will be probably at a max of 1.4v at 4.5GHz. I've used the eXtreme PSU calculator to get wattage, and the 500W seems to not be enough (I account for capacitor aging). Do you have any suggestions? I'd need to know if my amps per rail are fine, as well.

Thanks!