I've been playing with the video settings for a while to try and find something that gives me decent frame rates and where my eyes can actually understand what's being rendered on screen. For instance, I've had a really hard time seeing enemies at a distance; until now.
I'm not sure if this will work for everyone, but the solution I came to was literally to put everything on Low except for 8 x filtering and pumping up the super sampling to 2 x.
That alone has made the game a thousand times more playable.
Let me know if it works for you.