I would stick with the l can motors. You could run a 7xl on 3s and gear it up. The increased torque of the xl may make up for the lower kv and higher gearing. Not too sure in that situation, as I have not tried an xl in a smaller vehicle yet. You could try one of the ammo motors that tower has on sale, great price and the 36/56/2600 or the 36/50/3300 may work for your application. Can't go wrong with the price, buy both and give them a try!
http://www3.towerhobbies.com/cgi-bin...MO&S2=&S3=&S4=