Well, I was able to play around with it a lot more tonight.
I switched back to the 650M, and here's what I've found:
Terrain Tesselation and Terrain Shadow Quality refuse to be set above Low on any resolution I tried for both windowed or fullscreen (1680x1050, 1920x1200, 2560x1600). Shadow quality also refused to stay set above Low at the same resolutions.
I can set Overlay Detail, Terrain Detail, Water Quality, and Texture Quality to High at all the above resolutions and have not received a crash yet.
However, in my experience tonight, if Fog of War is set to ANYTHING other than MINIMUM it crashes. Sometimes before even one turn, sometimes in 10-12 turns, but ALWAYS crashes. When I force the Intel HD4000, I can run at maximum everything (except leader cut scene as you suggested) with no crashes...but it's obviously VERY slow. Maybe something about the fog of war code doesn't like Kepler?
I obviously didn't get a chance to stress each setting for hours on end, but in my experience playing for more than 5 minutes without crashing means it's not going to crash. Most of my crashes happen before the game even starts, but I did get to turn 14 once I think. All of the different situations I tried tonight got WAY past 14 turns without crashing...or crashed in less than 10.
I'll post up the crash info here shortly...