I'm gearing my E4JS by temp. If its too hot, I drop the pinion down a couple teeth. Run and check temps again until I hit the acceptable range. I've found so far I run pretty much the same lap times in TA trim with my SS21.5 from 4.2 up to 4.6 FDR. At 4.6 my motor is finally coming off around 145* or so. At 4.2 it was 175*. I'm going to try 4.8 for giggles. I would imagine that as long as I'm not hitting the RPM limit on the motor, I should see no decrease in lap times. I should also see more punch out of the corners. I haven't proven that to myself, but it sure sounds good.