Eric, what I meant about a 4 inch vise, was that you could clamp the handle section without the jaws contacting the fades. If you have a 5 1/2" vise, there is no way, without narrow, thick vise pads, that you can clamp the handle only, without getting out onto the fades.
I beg to differ about shavehorses being of "limited use" compared to a vise. I personally don't care for the parallel jaws on a vise, especially when trying to clamp pyramid limbs. I don't care that I have to work at a stationary bench that the vise is mounted to. I don't like chasing jaw pads around my work area.
But, that's the beauty of bow making, each person has their own preferences and styles, and tool kit that works for them.
Kyle