To the OP, you should be able to run it on Pc 1, but not sure how well. I have tried FSX with both an 8800gtx and 8600gt on the machine listed in my sig. The 8600gt was not handling things much worse than the 8800gtx.
With the same settings on both cards, the 8600gt still managed to maintain 15FPS, and considering this was 1680 x 1050 with 4xAA, it was pretty impressive.
The main problem with FSX is the CPU. It just kills all the CPU's currently out there. Service pack1 has improved things a bit, especially for dual-core, but it still is very heavy on CPU's.
I would say yes, you can run it, but only on very low settings and even then you might still get low fps.
I might suggest with those pc's you guys use FS2004 like my other half does. If you get the addons for FS2004 it looks almost as good as FSX, but runs far better. Although, some of the add-ons can cost a bit. If you are a regular Flight simmer the cost willbe offset by the use you get out of it though.