I know this is a bit old but I wanted to add my two cents...
The answer is yes (kind of), and it's because of the engine's volumetric efficiency (VE). VE is the measurement of the engine's ability to completely fill the volume of each cylinder. Having 50% volumetric efficiency would mean that at an arbitrary operating point, the cylinder is being filled with air (and fuel) at half of its capacity.
The volumetric efficiency curve will essentially resemble the torque curve that you see in dyno plots. What this comes down to is, around peak torque, your VE will be maximized meaning that the cylinders are being filled as much as they can be with air.
Thus, at peak torque, you will likely tend to have your leanest AFR given that the engine is fueled linearly with respect to MAP (manifold air pressure). Of course, with standalone/tunable ECUs you can tune your AFR to whatever you like and if you want to run it rich to be on the safe side, you're probably not losing much power (although you are using more fuel and dumping more crap out the tailpipe).
So I guess this only half-answers your question, as I'm not sure what would be the best AFR at each RPM point given the ability to tune the AFR at every point. It would be something to test on the dyno, by loading it up and playing with the ECU fueling curve to see what gives you best torque. So maybe I didn't really answer your question at all, but hopefully it will give some insight as to what is involved in getting an answer.