the 8150 will be better in highly threaded apps like video editing but for gaming get the 2500k or the 3570k as they will destroy any game you throw at them then the problem you have is you might end up gpu bound
Well unless your using mutli-threaded applications like say Video editing or certain 3D application I would go I5 all the way. That being said don't even look at the 8150 the 8320 is a better processor. Now if your looking to upgrade on the cheap right away it maybe worth looking at a AMD 6300 (or maybe i3) again an I5 is much better but there a new slot coming up in the next few months so if you get the i5 now its a dead end. While the AM3+ may have some life in them to upgrade down the road though I still doubt it would be as fast as the next gen processor that intel is comming out with. Also depending on your buget it could be worth it to save on the processor to gain on the GPU. Spending and extra $50-60 on the GPU and reducing that same amount to get a "lower-end" processor will almost always yield better performance in games.
For gaming purposes you will be very well off with the i5 2500k. The Sandy Bridge cpus are known to be very good overclockers. The same can be said for the AMD FX line but it is known to run at higher temps. Also keep in mind that the FX 8150 and the 8320 have a TDP of 125W vs 95W on the i5 2500k. Just keep that in mind. And I would also suggest the 8320 over 8150 because of it's newer Piledriver architecture that is an improvement over the Bulldozer, if you decide to take the AMD route.