Here is a nice gear ratio chart that Jimmy made or had made...
http://www.oople.com/rc/photos/revie...xgearchart.pdf
Had to leave for a second, sorry. Anyway, by leaving your 20T pinion alone and replacing your 96T spur with the AE 87T spur, you will lose torque but gain top speed. Along with playing with gearing on your car, you have to consider traction too. If you decide to adjust your gear ratio, make sure you will have traction. What I mean is, if you wanted to do the reverse of what you want (going from 87T to 96T spur), you want to make sure you have good traction or you may have wheel spin from having so much added torque. Loosening your slipper will aid in wheel spin also.