It is my understanding that the whole reason that stoich is what it is and the reason the computer adjusts the way it does, bouncing between rich and lean around stoich is to keep the cats happy and working and make them last, not to make the engine happy.
it's more than that, it's trying to guarantee reasonable emissions in general. an engine burning at stoich has fairly clean emissions, and the o2 sensors allow the system to be self-healing to a point (if there's a vacuum leak or something, the o2s can still force it to burn cleanly)

if emissions are a concern, keep it closed loop is a good idea