Vantskruv,
Just did the supposed Nvidia setting. This seems to be the solution. I'm flying at the moment with more FPS from 19 to 25 according Fraps.
My settup includes simheaven osm europe, HD mesh. I fly in the netherlands at Lelystad EHLE end fly on EHAM as wel.
Quit a filled in scenery.
Here are my Nvidia settings.