I have FS One and I think it's a fantastic piece of software and a very good, solid, purpose built sim.

FS One sometimes gets compared unfavorably (wrongly IMO) because it's not up to speed with the surrealism and eye candy in the 3D scenery graphics that some other sims have. For RC'ers looking for a proper sim, that can give a very wrong impression of FS One.

The graphics are good and like the whole sim are "purpose built" for RC'ers wanting to practice their skills. All visual elements that are relevant to this end (the pits area, sky, sun-glare, runway surfaces, the planes themselves, and sunlight effects on the planes' surfaces) are really well done. And like other sims, FS One has many photo panorama scenes which of course are real.

The focus of the FS One dev team seems to have been to just make a really proper RC simulation, period.

You suggested that your GFX card may not be very high end... FS One worked reasonably well for me on a very low end ATI 9250. I now have a GeForce 7600 GT (256 MB, 128 bit) and it works great with FS One. And I have only 512 MB system ram (on Win2K) and have no need to upgrade that... everything works smoothly.

I've been just psyched about what a good choice FS One was for me, so I don't mind sounding like a bit of a fan in recommending it

Good luck with your decision.

edit: Forgot that you mentioned you want to try flying twins. I don't think the current "Hangar Pack" has a twin and so would be contingent on a new Hangar Pack being released including one or more twins. You probably know that there are no user submitted planes... I'm guessing there is a very good technical reason for that, but I'll refrain from speculating in any detail.