10.12 and CCC2
I use a Sapphire Radeon HD4870x2, and I have used it for about a year and a some odd months (since a short time after it was released.) The only time it ran odd- slightly unstable was when using catalyst drivers near launch. THe driver disc included with Sapphire cards usually have worthless premature drivers that may not function at all (like the Sapphire HD 2600 Pro 512 MB AGP, it has PCI-e drivers included I believe) The cards both work perfectly now that I have found the right drivers THe AGP HD2600 just uses the AGP Hotfix and it always works great.
I used 10.9a since its release as a hotfix for the Dual GPU Cards HD4870x2,HD4850x2s and 5970 cards. It works beautifully, but I wanted to try 10.12 w/ the new CCC2 and it worked. The graphics weren't as smooth-they looked more aliased than the 10.9a's no matter what settings. I wanted the 10.12s to work I like CCC2. I want AMD to release an individual CCC2 download and I could uinstall it and the 10.9a driver and see if they mesh well. I will try 11.0 on release, but I think this 10.9a is perfect for gameplay. All games I play (All CODS) AVP, SC2, DAO and all DLCs, Spore, Chr. of Riddick-Assault on D.A. Far Cry 2, HAWX, DOOM3 and R.O.E., Sins of a Solar Empire. Only problem is the Overclock on 10.9a CCC won't downclock the memmory back to 2D sppeds. I have to use RivaTuner to O.C. 10.12 had a noticable framerate drop at times and and some stuttering. I run all options at highest detail w/ 4-8x AA and Quality Adaptive AA. on a 1920x1080 HD 16.9 LCD LG Flatron W2240T (same brand as in this techpower review test only smaller size) and my Rig is pretty juiced (see specs if you care) so I am pretty sure I can compare faults in the drivers, also I always clean install/ remove drivers with Driver Cleaner Pro and a cleaned registry.
Drivers 10.12 and 10.9a, 10.8b Do stop the problem of Regular 3D speeds running on BOTH gpus during 3D mode and drops BOTH gpus to 2D mode after the game exits. One of the most annoying and frustrating issues with dusing proper drivers for Dual GPU cards. As it is PC Gamer says an HD4870x2 is the 5th Best card on thier HOTTEST HARDWARE thermometer page as of thier FEB 2011 issue. Drivers allow it to be that way without the right driver the card only runs one gpu in 3D in half of the games making it a bigger, hotter HD 4870. I've installed DX 11 already, when more Direct X 11 titles release and make more and more use of the fancy Tesselation and Morphological AA and other stuff I will get a 5970.