Take a look at my article which is linked. The 6300 is more like a tri core with a physical HT implementation due to how the modules work. In other words, as it stands your P2 is better, as the 4300 is a step behind and the 6300 is a side step. If you're going to upgrade everything, it only makes sense to go the faster route, which would be the i5 3350p, or the 3570k. In gaming currently, the 3570k is king for price to performance, and the 3350p isn't far behind it. With Haswells release, there is no AMD that will touch the gaming segment crown to the 4650k once it's inflation drops mid summer.
Take note, we never mentioned the i7. Gaming does not use HT, and that same concept applies to the FX with its modules.