You can't "pull" a .63 unless you've got some really serious horsepower...... hence the .63 is basically a mileage gear.Just curious - why the .8 OD? Seems to be neutralizing one of the main benefits of the T5.
Don't fool yourself into thinking you're not going to see improved mileage with only the 650 rpm reduction of the .80 OD gear. It
is noticeable..... just not as much as the .63 OD.