If you got the Tahiti GPUs like the 7950/7970/280x the only miner I could get to work on V8 was XMR-Stak and the speeds are horrible compared to the RX/Vega GPUs.
Basically the most I can get is 400H/s while i've gotten 600H/s with V7.
What type of settings were you using before to get 600H/s?