Soldato
Could this possibly be the problem?
http://forums.overclockers.co.uk/showpost.php?p=27329543&postcount=5584
Could be, can't be bothered to try. Rolled back to 14.11.2 Betas and it seems ok.
I'll wait for the next Betas/WHQL or Microsoft update before trying again.
Don't think the drivers really offered me anything useful anyway.