Brandon,
I'm running fs2004 on Win7 64 bit and 6 gigs of RAM. Works GREAT! NO issues at all. Fast and stable. All my payware addons also work fine.
I have some older non flight sim hardware (slide scanner, etc.) that does not have drivers for 64 bit. That is a problem.... but it is clearly time to upgrade that stuff to the current century

.
My big problem is networking for the simpit. Win 7 and Win XP networking are not playing nicely with each other. THAT is a big headache for me. But it does not apply to the more typical flight sim person.
Can't say about fsx.... have it but it is not installed.
best,
............john

Intel i7 960 quad 3.2G LGA 1366, Asus P6X58D Premium, 750W Corsair, 6 gig 1600 DDR3, Spinpoint 1TB 720