well... lets see... to throw another loop in the deal here, if the 17t is running at full power to match the 12t the 17t will get hot, but so will the 12t because it should be going faster, and when motors dont max out and go around for a while at like half trottle they get realy hot. So what would get hotter... Hmmm... Theres probably some way to solve this scientificly but the real way to solve this is to just go outside and try it.
-Wes