BF4(w/ Mantle) runs great for me with my 280X and E8600 on a PCI-E 1.0 mobo. You definitely don't need a quad, or even a super fast dual to run most modern games at playable speeds. Mobo and memory speed are even less important. Unless you're an FPS(as in Frames Per Second) whore. Like most folks here are. I haven't found a game yet that I can't run at playable speeds with my system. But I don't have a huge catalog of games either. However, I do have a several that recommend Intel quads and 290X or better, and they're totally playable on my system. I do run my 280X super-mega-overclocked though.
Level of importance for gaming:
1. Graphics card
2. CPU
3. Memory
4. Motherboard
Having said that...you should still get the best you can get of each. It's always better to have more than you really need. If you can afford it. I don't recommend trying to find out how slow you can go and still get away with for gaming. I just have enough experience with "budget gaming" to tell you...it's likely a lot slower than you'd imagine was possible(CPU, mobo, and memory wise anyway).