Well, I certainly wouldn't run 6s on an 8XL. That's over 46k rpm! I was merely pointing out the max voltage of the ESC itself. Generally, 32-35k is the highest rpm for the XL motors as a rule of thumb. I would run no more than 4s or 14 cells for reliable operation. You might be able to get away with 5s if you're not maxing out the speed all the time. But 6s is a no-no IMO.