My experience is that Intel CPUs tend to run FSX better than the AMD ones. So I think your set is a very nice one for overall gaming, but FSX would be better off with an Intel CPU and only 4 cores than those 6 ones from AMD. It doesn't take much advantage out of the additional cores as 4 are more than enough to run it.

Take an Intel 'K' CPU which can easily be overclocked and keep the rest of the system. This should be a nice setup.  :)