I run 7870xt at 1100mhz (1.113v) and 750 mem for bitcoins ~505mh/s Happy medium undervolted and overclocked!
Scrypt runs poorly on these units 850mhz .981v stock mem ~410kh/s@ 20 I 16834 thread.
how are you getting 505mh/s out of it only clocked to 1100? all the ones I have Sapphires dont hit 500 till 1150mh/s
No idea, but I suspect yours are throttling. VRM temps get WAY too high at stock voltages and 1175 is the max I can run my cards at any voltage before they throttle down. Watch MSI afterburner and the gpu goes form 60-99% back and forth when the vrm's get too hot (even with a good gpu temp of 70c). Try setting powertune to 20% etc etc. and 375w is barely enough for that gpu. These babies have been known to suck nearly 300w each when overclocked at stock voltage, think 7950 territory. That plus cpu, ram mobo and I bet your psu is about to catch fire.

PM me if there is any other way I can help, that way we keep this thread cleaner.
I am running 2 of them at 1200Mhz GPU they are not throttling down they only throttle down when they get over 83C which these dont they stay below 76C, these 2 do 525mh/s steady and read 500+ consistently on slush stats, if they were throttling down they would be less than 450. They work perfectly fine at 375watts they have been balls out for 2 months now. the other one Used to run at 1185Mhz 510mh/s but after I had to reinstall the OS the driver is crashing randomly above 1145 doing 490mh/s with a 375watt supply. I chose these cards because the wiki page shows these cards drawing a max wattage of 175watts which meant they would work fine with a 375 watt supply. If you tach out the PSU it will shut down. I have played with these setups extensively.
anyhow I am just looking of any tricks on how to get the 3rd card back to the 1185, before I reinstalled the OS. It runs at the same Temperature as before no change but the OS happened