what size pinion you thinking of moving to? And what size motor, 480? Stock tamiya pinion in a 9 tooth, if you go higher number of teeth you end speed will be higher and you'll also have to
window the motor mount screw holes since the larger pinion has now moved the motor further from the gear. I'm not sure what the IS-2 does out of the box but you can find a basic speed chart
on the BAT site which also gives the distance to run full throttle so you can do runs at home to check. Just look in the Intel section of the site.
http://www.bayareatankers.org/