Don't get me wrong, I also don't have any monster card.I got gtx560 Ti and I have no need to upgrade it because it was running this very well from the release.But it's faster than your card 15-20 %.
Here is one video with 6770 and AMD Phenom at 3.6 GHz and you have beefy and fast CPU which is very good for this sim.
Note the date, there was few patches after that and lot of pilots with weaker
gfx cards reported improvements.
Just play with the settings a bit.
