In general you need both an adequate CPU and GPU. Depending on the game engine, either one of the two is more important. Typically either the game is CPU limited or GPU limited. If it is mostly CPU limited, it barely matters what resolution you use (you will notice a roughly constant framerate). StarCraft II for instance is quite CPU intensive due to its AI (it may have to render hundreds of units). Shooters and other games tend to depend more on a fast GPU. Frequently in case of Wine we see that display drivers can also be holding back games a lot (a lot of time tends to be spent inside drivers) holding back the GPU.
