Most games are currently GPU bound, with a few exceptions. The benefit of a 6-core vs. a 4-core phenom is based on whether or not the difference in price between the two can afford you a better graphics card.
Keep in mind that down the road, should you find yourself doing more and more Photoshop and multi-use office related work tasks that would benefit from extra cores, there is nothing stopping you from buying a CPU-only upgrade, as it looks like AMD has a very good future approach to releasing more and more cores on a single die without having to change the socket architecture (or at least maintaining backwards compatibility ala AM2+ and AM3), unlike Intel, who is caught in a loop of forever-changing mainboard architectures to better support more on-die features that AMD crossed the line on years ago.