Hi Chris, well done.
What I have read, anything below 10C for the Canons really reduces sensor thermal noise.
From what I found this was around 8C for my 450D so pretty close to what I read.
The Camera thermal load does blow out cool down rates...probably a lot depends upon the peltier wattage used and HSF's. Who was it...."Bert" I think made up a dual peltier cooler box. The extra device really helps. He also uses a proper PID controller. Speaking of controllers ....which I trilled
a cheap digital temp controller from fleabay.
It's only relay actuator switching but it managed to keep my cooler box to just on 1degreeC of the setting( camera in and running).