If memory serves me correct, the timing of the "valves" has, together with length and diameter of in and exhaust tracts, some influence on where peak torque and output is on the RPM range. And now I have to go back to "hillbilly logic" but AFAIK, advancing the timing a bit would place peak torque lower on the RPM range, retarding it would bring it up higher.
This is mainly caused by the closing point of the intake: The inrushing fuel/air mixture, as well as the column of spent gas at the exhaust stroke have inertia, and by shifting the valve overlap period, as well as the closing point of the intake a bit later, this inertia can be used to improve cylinder filling at high RPM when there is not much time.
Advancing the timing will basically FORCE the peak torque and peak power to occur at a lower RPM.

Retarding the timing will improve absolute peak power by shifting peak torque to a higher RPM, but that will happen at the cost of decent low RPM behaviour. Advancing the timing will improve low RPM behaviour (not performance) at the cost of absolute peak power. The length of the intake tract also has influence on this, but I am not exacly sure which change does what, and where in the rev range that change will have effect.
But I do have a nice video where this effect is demonstrated: My Wankel has a very crude muffler originally, that does little for noise reduction and even less for performance, but simply adding a length of completely random and untuned tubing to the tailpipe. has a very significant effect on peak power of about 8~9%

For what it is worth, I would not tune the engine for high RPM (increased heat) and I would not tune it for low grunt either (higher loads on the conrod), I would leave timing original, because spark ignition on its own will allready increase the engines ability to swing larger props at lower RPM.