Thanks Bryan.
I used an up cut spiral made of HSS and I was less than impressed with the speed of the cut...VEEEERRRRYYY SLOOOOOW and as you mentioned, the edges were pretty fuzzy. To achieve say a 3/8" dado, would it make any difference to use carbide and to do three passes with the first being 1/16-3/32", the second being 1/4" and the final being an additional 1/16" or would I still get fuzzy shoulders?
I used a typical bottom cutting single fluted bit and it gave a nice cut, but very little dust was collected from the cut.