I'm going to assume that the blue/purple missions are one time since I've gotten a couple for slicing now and they've only shown up once each as options.
Those missions did, however, give awesome rewards. So... no complaints here
I find that with my 540m at 1366 x 768 that I can set all to high except shadows. If I set shadows to high I can get greater than 30 fps easy... except if i want to move around or fight at all