I have basically the same problem, flying near a planet's surface always crashes the game after a short while - I have various mods but only a few parts mods (gamedata is less than 1GB, yet KSP uses more than 3GB right from the start?). Reducing ground scatter helped a bit, and reducing texture resolution is a short term solution if I want to finish a flight, but no matter what I do (and what mods I uninstall) it always crashes after a while. Flying in space has not crashed the game for me yet, it usually crashes when I return to the Space Center... Edit: "-force-opengl" as a start option reduces memory useage too, but drops the framerate (for me, at least). And press F10 if parts of your plane overheat.