Quoting myself because sometime overnight the hashrate once again dropped down to the 1170 range, so adding the "-c 4" switch and setting intensity to 5 (-i 5) weren't the solution. If no one else is seeing this behavior then it must be a quirk of my system - Windows 7 Pro / SP1, 16GB RAM, AMD Phenom II x4 955 CPU, 1x GTX 1080 (for now - a second is one the way).
Hmmm, annoying, that.
How much virtual memory have you set? Make sure your minium value is at least the sum of all gpu mem combined.
Then have a look at cpu load. If it's close to 100% it means it might end up bottlenecking your GPUs. Then you're sod out of luck. Some miners struggle with a nvidia driver limitation. Optiminer Zero for example is just unusable if you have anything less than a quad-core cpu...
I have manually set the paging file on my Onda board because, well... 6 GPUs and only 4GB of installed RAM, but I
assumed that with 16GB of RAM and just 8GB of VRAM I wouldn't have to mess with the paging file on this rig. This suggestion makes sense though and, besides, I will be installing a 2nd 1080 soon and that would have required tweaking the paging file anyway. So now it is set to 16384MB minimum and 24576MB maximum. Oh, and CPU load has been hovering just under 10%, so even the ancient AMD processor isn't having a problem here.