On a full tree the delay between the yellow and green is 0.5s. On a Pro tree it is 0.4s. You'll cut a perfect light if your reaction time matches these, and you'll red light if you cut the beam shorter than this time. Here is a primer:
http://www.staginglight.com/guide/react.html
On that race I sort of thought it'd end badly for our GT40 hero. I think Vipers weigh in much less than the predicted 3960lbs in the eariler post. I think around 3400lbs is more in line, so around 1500 Kg? So the real weight difference might be around 550 lbs or so, but the difference in torque is probably what - 300 ft/lbs throughout the entire rev range, not to mention the difference in hp......