While you've seen that contrast can interact with gamma, it's purpose is not to modify the gamma. It's just a by-product of the way contrast changes the overall light output.
If you don't have explicit gamma controls or a 10+ system, you simply get what you get.
Your best picture is going to be with contrast set correctly to the edge of clipping (at 255) that will maximize dynamic range and contrast ratio. Both of which are at least as important as overall gamma.
CalMAN Lead Developer