Hi, I'm on DP8.
I've run 10.8.5 just fine.
This is a Haswell 4770k Gigabyte Z87X-D3H and two Geforce 770's.
In ML they scale on voltage just fine.
In Mavericks always one of the two GPUs will stick to the highest voltage and stay there.
Notice how the ROP and core of GPU is so high vs GPU 2. I have tried disabling AGPM and switching the model type to iMac 12,1, many Mac Pros and the latest MacBook Air.
Any other ideas?