For pairing higher end graphics cards with lower end CPUs, here's an interesting benchmark where the 7970m graphics card was paired with AMD A10-4600M APU and compared with another laptop with 7970m and i7-3720QM.

http://youtu.be/YJecUDvJrfc

The A10-4600m is one of the top mobile AMD processors available, but it is significantly slower than the i7-3720QM. The extent to which the slower CPU would bottleneck performance depends a lot on the game, but it seems to be occurring with Arkham City, which is an older game and not especially CPU-bound compared to other, more recent games that are more optimized for CPU.