Not sure on the smoke, it could well be. You might want to fiddle with the graphics settings a bit and see if that makes a difference. Excessive aircraft can also cause lag, but the stock missions shouldn't contain excessive aircraft IIRC.
You might want to look at this article in regards to getting your controls right, it helped me
immensely:
http://mission4today.com/index.php?n...p=show&kid=261
mission4today is a great site for, surprisingly (
) missions and also skins and other fine things. Well worth signing up to.