RE: Motor Swap
With the gearing you have your power levels do not have to be anywhere near the specs of the two motors I mentioned, your right with an airplane you are dealing with direct drive to the loads for most part so the power requirements are much higher. I threw out those two motors because they are physically about the same size and weight as the one you are using. Unfortunately I don't have any experience with RC cars/trucks so I have little knowledge about the setups, however I do know of the advantages of brushless over a brushed motor makes it worth the effort to swap the brushed motor for a brushless were you gain 40% efficiency right out of the gate. You should have little problem finding a good substitute that will fit and work in your application. Where the power requirements are so low in your application you will find a lot of possibilities, go with the highest KV rating you can find and that will give you some real performance. For example a HiMax 5300KV may be a good choice, at 9.6 volts it will spin up to almost 51,000 rpm, if you know your gear ratio and tire sizes you could calculate your possible top speed from that. I would imagine your current gearing would work very well with any brushless motor that you could physically mount in this setup no problem at all and both your speed and duration on a charge would go up by quite a bit. All you need do to fit your current gear setup is use a motor with the right shaft size I would hazard a guess that you need a 3.2 mm shaft.
Depending where in MA you are located I can give you some local hobby shops that could give you some advice about you car. There is one in Hanson which has a lot of car parts and a good selection of motors and controllers in stock as well as knowledge about swapping out brushed motors for brushless.
For what it is worth I have run a brushed motor such as you have with a 3 cell (11.4 volt) li-pol battery with little ill effects for a year or so at this point but I doubt the brushes are going to last much longer...
Keep in mind that when using li-pol or lithium ion batteries, they require special chargers and will not work with with normal batter chargers.