I wouldn't plan on the speed or RPM's of the chart you found. The tire on that is much taller than you will ever use on your mustang. I'll repeat myself from an earlier post. I find that the 3.70 is very good but I almost wish I would have done 3.50's. As is is first gear is much better than when I had a T5 (totally useless then) but the 3.50 would give me more time to let the boost build up. For a N/A car 3.70 or 3.50 would be just fine.