Why would you run 12.8 when 13.4 works perfectly fine? Were 7000 cards even out when 12.8 was released? Did you ever consider that you are using drivers that were never intended for that card? Have you also considered that it is why they have released newer drivers? To fix issues?
Actually 7xxx cards are supported since 11.12 (8.921) drivers.
Also AMD interest is in fixing
gaming issues.
A newer driver could be better at gaming, but not necessarily at mining.
In fact, older drivers = better drivers.
Maybe try Linux? It's so easy.