I run the 825 on 6S on the XTR. It's straight bonkers. 0-60mph in 3.8 secs on stock gearing and Onyx batteries.
Put simply, I simply don't feel any need to replace this motor/ESC combo. Corally have a long history of making good brushed motors and speed controllers, so it figures their brushless offering are bestowed the same magic.
However, it gets toasty on 6S. You have to use fans/heat sink to manage the heat. Then to protect the fans (especially if you run on grass!!), you need a chassis shroud to stop crap from getting into them. Or buy lots of replacements!!