I've never successfully gotten nVidia's control panel to apply an OC for me on reboot. Maybe it's just me. But that's why I use MSI AfterBurner, which is really just a skinned version of RivaTuner.
Auto might set the slider to 40%, but it's really a temperature-controlled fan speed. Unless you're trying to get the GPU temp down lower and can live with the noise, you might as well leave it be. If it's getting really hot, auto will crank it up anyway.
But if your'e really looking for more memory bandwidth, why not just try to turn up the VRAM without adjusting the GPU? Then you can see if that theory plays out. You may find you don't want/need to turn up the GPU clocks at all.
I do not understand what I do. For what I want to do, I do not do. But what I hate, I do.