AMD's GPU drivers give you a decent range of control over board power limits, fan curves, GPU and memory clocks and voltages, and on at least some models the ability to fine-tune the shape of the voltage/frequency curve used. Really the only thing missing is an automated tool to explore the V/f parameter space to find the limits of stable operation for your particular chip.
I'm using the software that came with my card to do that. It makes sense that the graphic card manufacturer's would ensure stability with the cost of it running hot - by undervolting I'm playing with potential crashes and that won't do for a card defaults settings.