I owned a Core2Quad Q6600, overclocked, awesome chips. But they're not the same with today's games, even cheaper chips such as the Sandy Bridge (LGA1155) Core i3's and Pentium's outdo some of the old Quads, and i've owned both so i can agree with the benchmarks.
When i was moving from LGA775 to 1155, I sold my Q6600 plus a mobo that was like new for $140 all up on eBay, which barely bought me a new mobo. This was just under a year ago too.
Here's some benchmarks between a Q9650 and an i3 3220
Pretty close, eh? Though the i3 is a dual core and one of the cheaper CPU's, still good for gaming. Better than the Quads at least.
How about a Q6600 vs a Sandy Bridge Pentium like i said before?
You can see, for less than the price of a second hand Core2Quad, the Pentium does even better.
Those quads are still going for around $70+ on eBay, depending which one. For the same price, you can pick up an LGA1155 Dual Core (not the Celerons) and get the same, or even better performance.
There arent many brand new 775 mobos around these days, and for the same money or less you can pick up a H61 or B75 1155 board.
Unless you're getting the quad for <$50 then you should pass it up and move onto 1155 or wait up for 1150/Haswell chips.
EDIT: forgot to add, my OC'd C2Q was still a huge bottleneck to a GTX 560 Ti. Wouldn't be any better to pair up a similar chip to a faster GPU like the 480.Edited by PoisonousRakija - 2/23/13 at 2:31pm