Really, CPUs will only give like a 1fps difference in gaming. I would actually say a 2500k is the best gaming CPU, or a 2600k with HT off. That way windows doesn't have to try to even the load out across slow threads.
But your CPU should be fine for gaming, what clocks can you reach? The main thing with BD is that it will have "modules" instead of cores. As I understand, each module is equal to about 1.8 physical cores. So I'm not sure if the game will see a module as a core, and utilize all 4 modules on an x8 BD chip, or only use half of the modules.
But really, if you looking into more gaming performance, checkout another 5850. They might be slightly bottlenecked, and that will be the time to upgrade your CPU, but BD is rumored to be the king at multi-threaded things, like rendering and encoding.