I use Aoclbf 1.81 + Phoenix 1.7.0 whith modofied kernel + Cat 12.1 + Windows 7 x64 SP1
i tried cat11.12 installed on cat11.11 / 2 x 6990-rig
multi-gpu-cpu-bug solved BUT hashrate down ~ 5 %
cat12.1 seems to have the performance of 11.12
maybe you have to go back to cat11.11