The one thing which occurs to me about the narrowing of beds to 3' wide instead of 4' wide, given that putting edges on beds is a relatively fixed / permanent thing, is whether all of your beds would be this narrow, or you'd leave some wider. I would struggle to grow more than 1 row of spuds in a 3' wide bed, once the space for earthing up is taken into account, but could easily get two rows in. So it might depend on what your other plans for cultivation are, if any.