I like Dirt 3 a lot, but I don't ever remember it crashing when trying to exit the game as much as it is doing with my setup now. I've added it to Steam as a Non-Steam game, don't know if that has anything to do with it, or maybe it's Windows 8.1? When I was installing the game it threw up a whole bunch of compatibility warnings about GFWL.
I also have Forza 4 by the way, and I rented Dirt 3 out on the Xbox 360 before I bought on PC (2 years ago!) I remember Dirt 3's graphics being better than Forza 4's even on the Xbox and obviously Dirt 3's graphics on PC are better than Forza 4's graphics on the Xbox.