Help me understand.

[_paralyzed_]

since you are running the mm i'd go with the 2600kv. you are limited to 4s or 12 cells with the mm, (some have run 14 cells or 5s, be careful!) so the motor is closer to the sweet spot (35,000rpm) with the 2600kv, an overall matched system where you would be under volted with the 1800kv. on the speed calculator balooning doesn't really matter and 6 is a good number for a revo diameter