If your looking for a bit that will give you a great finish on top and push the material your routing toward the spoilboard on a CNC router, then a quality down shear spiral is what you need.  These bits are often used for rabbiting and dado grooves, because they leave a nice finish on the surface of a dado.

B.A.M., Inc.

PO BOX 12711

Salem, Or 97309

Phone: 503 362 8587