more efficient?
 

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.

Too low of an rpm may cause a little cogging at startup if anything. But efficiency should be fine. If startup and top speed is fine then I'd leave it as-is.

so I wouldn't see any benifits with the 2.5? as far as heat and runtime?

Not really. Your setup requires X amount of power to run like you want. Whether you use what you have or use a different motor geared for the same speed doesn't matter. The output is the same.

I understand that, I just wasn't sure if the motors worked their best at a certain RPM, I know that to high of an rpm can be bad, but wasn't sure if it was reversed.

Thanks Brian, and BTW your gearing page rocks!