Obviously, if you read between the lines, you'd see that by retro I meant things within a few years of the CPU itself's release. So anything from pac man right up to about Battlefield Bad Company 2.
I would never pair a 580 with a C2D. I had my 580 paired with my 2600K and that was a decent combo. I don't think I'm exaggerating when I say C2D is severely outdated.
Nehalem improved the performance per clock over Core 2 by what, 20-30%? Then second gen i7 improved it again by like 30%. Since then we've seen tiny increases, but that's a pretty big difference.