CPU required depends on the specific game in question - - they all have different hardware requirements.
So whether you need a faster CPU or not depends which model CPU you have now, and which game you want run.
The GPU is also very important for decent gaming performance, not just the CPU.
Editing graphics can be done with just 4GB installed RAM - even if using Photoshop CS3 as I do, and my system only has 4GB RAM (Windows 7), yet I can edit even hi-res images quite comfortably.