Thats a good way to put it, basically anything higher than a 6670,7670 (oem) would not work well together to make it beneficial. Kind of like with nvidia and phsyX. U can use a 670 GTX to do just graphics processing and a 9800gt to just run physX, but having the 9800gt run just that it actually lowers fps drastically if you had just the 670 doing both the graphics and physX processing