Mark,like Lee,both wood and wire our used on our rats.
Mike does the larger rats on wood---6 1/2 inch base.When the wooden stretchers are full we both use wire.I have found that most wire strerchers come out with finnished rats about 6 1/2 inches wide,though I have one batch of wire that are wider,and I only use those on huge rats.
There is no question,that rats look and feel better,when done up on wood.But I am keeping my supply of wire ones.When you need to put up a bunch in a hurry,wire is the way to go.
As of last year,monetary returns have been pretty much the same,on both types.
Tom