Have you tried increasing your fan speeds, 11% at 70C is a bit low. Because I am guessing the cards are running too hot and that is usually the reason my cards slow down at-least for me. (I usually start my cards off at 50-60% and let it gradually increase from there).
Or another way to lower your temperature if you have not done it already is lowering your voltage and maybe even adjusting your core/mem would help as well.
I wouldn't mess with your breaker, unless you actually know what you are doing. (because it depends how old your house is and what wires are being ran through it.)
Depending on your home most rooms run on 15AMP or 20AMP breakers per room @ 120v (mostly for united states).
A quick breakdown: If your room is 15AMP = 1800Watts for that room, then 1440 Watt is 80%, 20AMP 2400 Watts for 1920 Watts for that room (80%), which when running for long periods of time you want to keep your wattage at 80% of the breaker.
Do you know what the amperage is for that room? What else are you running in that room?