Thank you all for your response.

I figured that my pc was high end relative to the game (reading the recommended specs), of course it's not a high end generally.

The thing is, lowering view distance had a huge effect on performance in cities and it runs much better now, although the distant planes look a bit boxy now, but I'll live. Unfortunately I can't afford a new rig at this time.

IL-2 isn't really like a normal game. It'll suck up almost as much CPU, RAM and GPU/VPU processing power you can throw at it. Sort of like some of the professional editing software like FinalCutPro or Photoshop. Simulators will work alright on the recommended software but years later will be the time when they can be fully appreciated.

That said... I have a reasonably top spec system (Core i7 870, 4GB of DDR3 RAM, and a nVidia GTS250 with 512mb) relative to the highest performers out there currently and cities still drop my FPS. Part of the problem is engine related. It was explained by Oleg years ago and I can't remember what it was... but something to do with the core fundamentals of how the IL-2 engine references and draws objects means there are slowdowns even with the most powerful systems. Case in point was the Final Days benchmark track that was hanging around here last week - the best anyone got to date was 11 fps on the opening sequence. I got 9 fps. It's murderous :) At that point you can blame the engine rather than the PC.