If you have a board that is running at 800gh and pulling 570 watts, you are getting close to the limit for the PCIe connectors. To try and cool it off I would recommend trying one or more of the following: 1) more powerful fan on the radiator (stock is ~.33-.5 amp, try to find a 1 amp or bigger) 2) point a fan at the VRM (the space between the pumps) 3) find a cooler location for the unit. I'm curious, are you using BFGminer or CGminer? I know there was talk of commandline underclocking of the units, but I don't know if either program has it implemented as yet.
I'd rather underclock it instead of trying to desperately cool it generating tons of noise in the process, but I'll see what happens. I'm using cgminer 4.6.1 on Linux.
BTW, these units seem to get excited and run faster and hotter with a powerful PSU instead of a weaker one. My 550 GH unit runs cooler and slower (650 GH/s, 420W) when I power it off my 500W Super Flower PSU instead of the Corsair TX850W (690 GH/s, 470W).
EDIT: Swapped the Corsair TX850 to TX750 just now. Why? I don't know. And I put a fan blowing towards the power parts
http://i.imgur.com/JvVzNII.jpgGH/s went down a bit. Power draw 550W. Temp at 70.00°C after a half an hour and no thermal throttling so far. So what I got with my two Monarchs is 1.45 TH/s for 970 watts which is not bad, but I'd still underclock the faster unit for less heat and noise. Although the two combined are still more quiet than a single Antminer S3 underclocked to 420GH/340W.
I wish I had an answer for you on underclocking. Have you tried running the faster one off of BFGminer yet? You mentioned a speedup with CGminer on your 550, I'm curious if it will run slower and cooler and if there is as big a difference in speed on the 700.
