I have fixed my HW errors by doing a clean removal of 14.6 drivers and installing 13.12.
Currently hashing at 2.5 MH/s with 1075 core OC.
EDIT: an hour later the system froze. I didn't have this problem before with X11.
14.6 is in beta, 14.4 is more stable.
With 14.4 I get horrible performance on n-scrypt. So I guess 13.12 is for now.