[lincpimp]

I would say that a lower kv, like 1600, for larger motors such as the 1521 and 80mm medusa is the way to go. You get more torque from the longer motor, and lower motor rpm generally leads to better temps, and increased component life.

Now you may want to stick with a higher kv for a smaller motor, as the increased rpm will help out with less torque. This assumes you are running the motor in a heavier MT.

I run hacker c50 xl motors (longer than a 1515, but not quite a 1521) in 10 and 11 turns. Those are both near 1600kv, and work well in my heavy lst2. I have a 1521 to test as well, just waiting on some hex pins for the 20mm hubs so that I can run taller lst2 wheels/tires. And some al knuckles too.