Hi, this my speed (2x480 XFX)
Version 6.3:

Version 6.4,7.0:

Speed down on 0.8 MH/s ETH and 10 MH/s on DCR per each VC, with the same others parameters.
Is it normally?
Try different drivers, may be it's the reason, also you can try to set "-etha 2" option.