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.