I just assert that it's not worth it to worry about, really the motor plate has a very small surface area and an even smaller heat conducitve contact patch with the motor.

The cooling of the motor is done by airflow through and around the motor itself, the motor plate might be worth two degrees. According to my handy-dandy heatsink calculator, with a heat gradient of 50 degrees C and a cooling air velocity of 5 meters per second under perfect conditions the motor plate is worth about four watts of heat lost, the real value is probably less than two watts. Under the same conditions, a real motor heatsink with ten two-centimeter square fins (smaller than most touring car sinks) is worth 50 heat watts. You're not doing any cooling worth talking about through your motor plate, its really more of a heat dump in that it doesn't have enough surface area to effectively get rid of heat.

This isn't to say it doesn't do some good, but if somebody ever tells you that switching to a different motor plate dropped ten degrees on the motor they're probably incorrect.