what gearing for E-revo/1515/1y on 4s and 5s

[shizzon]

im trying to find a solution for running both 4s and 5s in my E-revo, so basically a happy zone for both my 4s and 5s setups so i wont have to go changing my gearing every time i swap packs.

from playing around on the top speed estimator as well as calculator it seems that on 5s the truck will run anywhere from 8-10 mph faster for any gearing setup than it does on 4s. would it be ok to gear the truck for about 40 on 4s and 48-50 on 5s be acceptable. The batts being used are 4s 30c 5000mAH polyquests and 5s 5000mAH 25c RCM lipos (according to many on here they are under rated and are capable of more than 25c).