more efficient?

[spcpicard]

I am currently running a 1512 3d in my losi 8 on 4s which seems to be perfect for me, but due to the low rpm, am I loosing efficiency? Would a 1512 2.5d run cooler and more efficient geared at the same speed (38mph)?

FYI, I ran a 1509 2y this weeked for 2 10min runs for practice, the 2 5 min qualifiers and on the 3rd 5 min qualifier it went up in smoke. It felt really good but I guess it was too much for the motor and it was running pretty hot from the get go. I had to put the 1512 3d back in for the main.