FPS hog in this senario
 

I've added the latest tweaks and getting great fps , making massive air battles ect. One massive bottleneck I get now is when say , a squadron of Spits / Hurricanes are attacking bombers with tracers flying everywhere - the game will struggle but when you pause it the fps are smooth as silk again. Anybody know whats causing this? is this physics related with bullet impacts?

Do you mean the FPS are smooth whilst the game is paused? If so nothing is being calculated so it's bound to be smooth.

Or do you mean if you pause and then un-pause the FPS improve?

If Machoo mean the latter, I had the same experience in IL2, particularly when flack opened up. It seems to me IL2 has problems keeping up sometimes, and pausing it allows the computer time for all processes to catch up, so that when resuming it runs smooth.

I don't know much about computers, and my experience is with IL2, so I may be miles off here.