You can use a return big enough to drive a bus through and it will not matter, since you're using a return regulator as the return orifice. "Whatever" the size of that orifice is inside the regulator is the restriction. So, running a 1/2" return is total overkill, and probably 1/4" is as well, although that's what most run. It's like exhaust. You can put a 2.5" pipe on a slant six, but unless the manifold outlet is the same, any benefits will be minimal, to non existent. You can listen to the "run the biggest return" guys all you want, but you're wasting your time, since the regulator IS the return orifice. Unless you have a total badass race only car, the biggest return line you will probably ever need is 1/4".
