[aqwut]

7XL, has higher KV (rpms/volts), so you gain more rpms from less voltage, but amp draw is higher, and produces more heat...
10XL, has lower KV, so you gain more rpms from more voltage, but amp draw is less, and produces less heat. more torque on low voltage.

7XL, 8XL, 9XL, 10XL, 11XL.. they're all capable of the same kind of power... just whatever tickles ur fancy...