Thanks MigBuster,
I think I'm experiencing the same glitches that were described by stuntman and viper63a earlier in this thread - flickering models, parts of terrain dissapearing for a while, and some plane parts "exploding out", especially in external views. These glitches are particularly noticeable just after loading and starting a mission, it tends to go away 1-2 minutes after starting to fly. I'll try to attach some screenshots showing the problem.
Yes, I have a modded install, I have Stary's mod for terrain.