The Quad Core 2's are still very good CPU's. They still go for quite high prices on the bay 2nd hand. Its more about the GPU these days with games, mid to high end last generation CPU's are more than enough for new release games today.
Very good is an exaggeration. They're good for certain uses but they're very old now.
FPS goes up a lot with a fast CPU in modern games, it's certainly not a case of it being more about GPU.