In your Kelly Controller user manual (yes, I know most would rather lose a testicle than read a manual) there are settings for motor current (called phase current) and battery current. These are expressed as percentages. Phase currents are based on battery current, and a good phase/battery current ratio for a hub motor is 1.5X - 2X battery current. Your controller, using PWM (Pulse Width Modulation) converts battery current to phase current. Phase currents are much higher than battery current when accelerating, but become the same at mid-throttle. If you are really bored sometime, there are graphs depicting phase current/battery current through the throttle range. Phase currents are the "torque" you feel on take off that makes you scoot back in your seat.
OK, that's a lot to take in, but I told you all of that so I could tell you this: I'm sure your phase and battery currents are set at 100% in the user program. Since you have conquered the milestone of speed, perhaps you could play around with these two variables to try to maximize your efficiency. Any energy spent in excess of what is needed is lost to heat. So if you get these two settings right, you should see the same performance with lower temps on both your motor and your battery. It will extend your battery life and keep you from spending more time and $ on an exotic solution.