I just read an article that implores us to limit the number of mix files that we create for a multi-track project - for the sake of our sanity. As a rule of thumb, Joe Gilder stops after he has created the 3rd version of his mix. There isn't any real science behind it, but I agree! It's easy to obsess and tweak until you're on the 15th (or more!) version, and there is no logical end. Typically any improvements you make after the 3rd try will be insignificant, especially when stacked against the extra time and stress involved in creating the 4th through the 15th versions. so do yourself a favor and stop yourself after 3. You'll be leaner (your processes will anyway;)) and less stressed.
Here is Joe's article: http://www.homestudiocorner.com/power-of-three/