Assuming my CPU puts out about 100W, I have a total load on 9 heatsinks of 163W + heatdump from pump, 170W.
With one more TEC and going 4V -> 5V, power will 109W to the TECs. System total will be 46W higher, 216W. Thats a 38% increase in cooling power and a 27% increase in heat output. With 11% more heatsinks.

I have just taken a regular inside/outside digital thermometer and plunged into the reservoir. And the temperature does not match what Everest shows. Water temperature lowest is 15.7C, 23C ambient. And it seem to stagnate at 21.5 under load. This is a cheap thermometer. But I doubt its scaling is off by much. So temp rise 5-6 degrees C is about right.
But the CPU temps are probably way off.