The FX8120 has a turbo speed of 4ghz but it's still has really weak single core performance and that will hurt you in some games.
I never noticed, most games use more than 1 core but will that be an issue that is worth upgrading over? I do have the hotfix for windows 7 installed btw.
As others have said- keep the 8120 for now, the performance difference between bulldozer and piledriver isn't that big (10 to 15%). If you need more its an unlocked chip so overclocking is realyl simple and you can push it quite a way with better cooling.
Yes but how easy is the overclocking once I've bought a stock cooler and do I need to even overclock it? some people are saying that I don't need to but 3.1ghz seems a bit too low to not bottleneck.
Well you would need to look at a better air cooler however they shouldn't cost you more than about £20. As for overclocking- easiest way is to change settings in the bios. To speed up any FX chip all you need to do is increase the 'cpu multiplier'. However as CTurbo has sated that CPU isn't 3.1 ghz exactly. It runs between 3.1 (minimum) and 4ghz (maximum) speed.
I would only suggest over clocking it if you're actually having a problem running something. The PC I game on most is a first gen Core i5 laptop that runs at 2.4ghz and yet modern games (e.g. Tomb Raider 2013, Star Conflict) run fine. It does depend on what you play- however normally the graphics card will bog down before the cpu becomes much of a problem.