as aevm said, it's all about the cpu. for flight simulator, definitely get a quad, the fastest one you can afford. any P43/P45 board should be fine. As for gpu, a 4850 is more than enough. you could probably get by with a cheaper one. and definitely get 4GB of ram. fsx needs alot of memory. to make the most use of the memory, make sure you get a 64-bit version of windows.