I had the 2300 kv motor. If you kept the gearing at 14 tooth or lower pinion, the heat would be reasonable. Any higher and it would heat up hot near the end of the pack. The 1521 is the better choice. Put some spacers under the motor mount for clearance and you are ready to go. I just ran my 1521 with some Jumbo Kong tires for fun. My Fastlane super thick outdrive dogbones actually twisted about 90 degrees on one wheelie! Ungodly torque on these motors. Also, watch your foams. It sounds crazy but stock Pro-line foams will wad up and deform after a while. Do they make a molded foam for the 40 series?