My system: P4c 3.2Ghz, 9800XT, 1Gb Corsair DDR-XMS PC3700, P4C800 Deluxe
I was getting around 16-25 flying round the airport in spot view. I have installed loads of PAI with the default removed if that makes a difference. Its a Demonite (which I shall take the opportunity to say - Don't buy anything from them!).
I am running a network (not actually working but still buzzing away whatever) with all sorts of guff in the background, filled my harddisks and I haven't defragged for a while

What sort of tweaking do you do? I havent done anything! Perhaps I should think about reformatting and starting again...........
Could you post a screensot with your FPS displayed so I can believe it!