gollumist, qqqq, thank you for your answers!
hmm.. 3.4 CPD is very small. I thought that it would be the same as hd7850 (4.7 CPD).
Yes it is small - normally R7 260X is 1/3 of R9 280X. I try it for a lot of algorithms X11, X13, Eterum and gives around 1/3. Only for quark gives a little bit more than 1/3 of R9 280X