hey fun4ej, try these motors for your cat, they should bring it up to 40mph with two 7 cell packs in parallel.(don't try series, it might blow them)
http://www2.towerhobbies.com/cgi-bin...&I=LXNMM6&P=ML
these are different than the ones that you have, because they are 12 turns instead of 19 or 20.