Yep if you have a 4870 get a better CPU then the extra L2 cache makes a difference on games right now. Get a Q9450 or Q9550 as some games benefit from the quad cores as well and in future this may improve as well. Remember most benchmarks use the quad core to generate some of the score but real world results count and extra L2 cache on the CPU will help a bit.
Yep, you only have to look at the top ten Far Cry 2 benchmark scores to see that quad is the way to go.