I'm not a gamer, not even a casual one so my system was built specifically for rendering in CPU and GPU as I use both DAZ Studio and Poser, I also develop add ons for both using Adobe, Z-Brush and 3D Coat.  I use Luxrender too but I'm looking at Octane for realtime renders and animation.

 I thought you shouldn't mix Kepler with Fermi or that at least it wasn't recommended.  I also had been told that the GTX 580 was the fastest card for Octane so that is why I went for that one twice.  I hear that Kepler is coming thru now but I still see the developers using GTX 580 in the Octane forum.