My experience is the same as restless. On my two gigabyte 270OC, 9.7 is still the best.
11.0
-h 448 -dmem 1 (11.0 default) - OpenCL hang.
-h 512 -dmem 0 - 840h/s
-h 256 -dmem 1 - 810h/s
9.7
-h 512 (default) - 855-860h/s
You get 800h/s from 270 oc-ed ?! What clocks ?! Frankly I don't believe it
I get 480-500 from 270x running 1100/1500...
I also get hangs sometimes with 270x and 11.0 - when the card is main one running the display under Win10. Same card under Win7 runs fine 0-o