I think the brain might be thermally limited so adding more fuel to the fire could only do so much. Maybe future humans will have to take up a lot more copper to deposit in the cooling veins.
If you beat the heart a lot faster you probably get pretty good cooling. Vent that in the extremities and start sweating. There is obviously still a limit but in day-to-day life we don't even really come close to the brain's cooling capacity.