Will,
I have drilled lots of holes (into plywood) using my cnc router table. It has a variable speed spindle with a range from 8000 to 24000 rpm. The main thing is that I am limited to drill bits or cutting tools that will fit into one of the collets. Of course smaller router bits can be used to make larger holes using circular interpolation. I have 4 sizes of collets: 1/8",1/4" 3/8", and 1/2". I have seen others who have mounted a second Z-axis slide and installed a variable speed electric drill for slower speeds when drilling into metal.
David