Pixel response time is a related concept to framerate but more about how long it takes a pixel to change from one color to the next. Usually measured in cycle time from grey to grey again, a low rate just means that images will be smooshy looking, have unclear boundaries, and end up with a 'motion blur' effect. So even if your mbp supports a reasonable sounding 120hz (8.33ms for a full frame sweep), some of those pixels will still be in transition when the next frame hits. At least, my take on it as a somewhat casual gamer.