Hi, I'm just a noob so go easy on me
In comparisons of the AMD HD 6990 and Nvidia GTX 590 the best performer depends on the particular game being played, so I was wondering if there are any motherboards that allow you to have both AMD and Nvidia GPUS on the same Mobo at the same time and easily switch between the AMD and Nvidia GPUs to suit the particular game being played?

In comparisons of the AMD HD 6990 and Nvidia GTX 590 the best performer depends on the particular game being played, so I was wondering if there are any motherboards that allow you to have both AMD and Nvidia GPUS on the same Mobo at the same time and easily switch between the AMD and Nvidia GPUs to suit the particular game being played?