Low FPS in cities on a high end PC

[The Stalker]

It's a performance problem in my IL-2 1946 (4.09m).

Although I have an Athlon 3800+ dual core at 2.00GHz, 2GB of RAM and an Nvidia Gt220 1GB (which should be more that enough) whenever I approach a large city in the game (eg. Berlin) my frames drop to 10-20 or worse. It makes ground attacks nearly impossible and it's annoying as hell.

I tried different settings but nothing helped, and it doesn't make much sense to play the game on medium settings with this pc. My guess is that it's an optimization issue, but I can't find the cause of this.

If anyone knows what might be causing this please help. It's such a great game and I should be able to play in on maximum settings without problems. I play single player on 1680x1050.

Thanks