The frame rate ranged from 10 fps to 60 fps, but probably averaged around 14 - 20 in combat.
Turning the cockpit off gave as much as a 2 x increase in framerate. This wasn't a problem for me as I usually alternate between padlock view and no-cockpit view in combat.
Running in 600 x 400 and 1024 x 768 made no difference at all to the framerate! ( Credit the Banshee card. )
On a 15" monitor 600 x 400 gave as much detail as I needed ( see the screen shots in this diary ). As you turn up the resolution the screen fonts get smaller so I would probably only use the higher resolutions with a larger monitor.