It looks like you will need to do some work just to beable to put water cooling on it, without water cooling I can't see this motor taking much more than 8.4v unless your doing lotsa breaks to let the motor cool down at higher voltage.

If motor is too hot to touch or is melting through your hull you may have found the limit.

voltage isn't just limited by how good the esc is, it is also limited by what the motor can take. What make and model is that?

Ivan.