Hi ArcadeAction,
By looking at your log, I'd say GM is crashing right at the point where it switches the video mode. This would happen if DirectX was not available for some reason, maybe because the functionality has got corrupt in the previous GM session.
Just to make sure, when you tested disabling multithreading, you tested it right after start, didn't you? This is important. It would be good to see a new log with multithreading disabled.
It would be a good idea to test GM v0.152 too.
BTW, if GM can start multiple times when run from command line that means it's perfectly fine. It's how HS interacts with it what's messing things up.
The fact that the new card has exposed this issue doesn't mean the video card is to blame, maybe the initializacion process of this chipset takes a slightly different amount of time and things happen in a way that result in the crash you're seeing but the actual cause of the crash was previous. Of course there's a remote possibility that the card as actually faulty but I don't believe so.