FMS is fun to play with, and it is a good tool for beginning pilots to practice learning "toward" and "away" orientation, but it's not very realistic at all with regard to overall flight physics.

Real Flight offers downloadable demo versions of G3.5 and G4. You should give them a try to see how well your PCs will run them. I mentioned the Clear View flight sim earlier in this thread, and I believe it to be a very reasonably priced product with good physics. You can download the trial version of Clear View at http://www.rcflightsim.com and then register it for $39.99 to unlock the full version if you like it and the demo runs well for you.

As previously mentioned, Clear View works perfectly well with the ESky USB sim controller.