One thing you need to be aware of is that because of the way game software tends to work, you will (usually) get diminishing returns from having more cpus/cores.
This is because in order to get the full benefit from multicore, you need to have multiple threads which are roughly comprable in terms of how much horsepower they require.
The problem is, that some threads (typically rendering, physics etc) are vastly more demanding than others (networking, input) and so you will have your physics thread running at 100% while other threads are only using about 5% capacity.
Optimising for dual core is therefore far easier / more efficient than for quad, octa or whatever because only a couple of threads are probably taking up 90%+ of the cpu time.
Obviously one would hope that in the future quad+ core support would allow us to have much more advanced AI due to having a core/thread dedicated to it. The trouble is of course, the biggest limitation on AI is more to do with the lack of good enough code rather than computational power.
