I thought FSX was kind of optimised for dual core but not quad core.
I've read something along the lines of "it will use one core most of the time, 2 cores sometimes and the 3rd and 4th very rarely/not at all".
The consensus from a thread I posted a while ago wasn't really clear, but in the end it was three votes for dual and 2 for quad.
If you get the Q6600, the try and get your hands on the G0 (Golf Zero) version, as these are widely known as the best, most stable, most overclockable version of the Q6600.
I would say E8400.

