I didn't test this with frame rates or anything, but will tonight.
The game appears to run much smoother if I log into steam offline.
Far fewer stutters and generally much smoother, with everything on very high and 8xAA in game.
I tested this battling over water and then crash landing when trying to get to Manston with a duff motor, so better performance over both water and land.
Can anyone else confirm?
Thanks!

Dutch
i7860@ 2.8GHz
6Gb DDR3
Ati 5770