The reason I'm going for 8 GB is because I plan on this being a mid to high-end computer capable of playing games like Fallout 3 and Age of Conan. I have 4 GB now and still run into Memory Allocation Errors at times, so 2 certainly won't be enough.
With the PSU, and the Corsair/PC Power & Cooling ones, they're the same price? Unless you mean before the main-in rebate, but I plan on doing that anyway.
As far as the bottleneck your talking about, I seem to be missing what the problem is. On Newegg a good 80% of the reviews report running with 8 GB no problem. I do see what you mean about a Quad-Core being better, they seem a bit pricey now, I'd rather wait until the technology developed more and they come out with better, cheaper ones, then just upgrade then.