I have a 6" and an 8" bench grinder. The wire wheel is on the 6" one. As the wheel diameter increases, so does the surface speed of the working area. I'd be spooked about using a wire buffer on even an 8" machine, since the brush will yank stuff out of your hands unless you're holding it with vise grips or something similar. For detail work on small parts, I use a 3" diameter buffing brush in a hand drill motor, with the drill clamped into a vise. I also use extremely fine wire brushes with .002" diameter wires for "carding" rust blued gun parts. Some of them are tiny, like screw heads and trigger assembly parts. In my decidedly biased opinion, based on only 60+ years in shops of all types, "Smaller is better!"
Jerry
