I assume you are talking steel gantry. That's heavy. What size ball screws? What are you going to use for a spindle on the drilling axis?

I ran a little test today and it requires between 300 - 500 pounds to make a 25 mm hole with an annular bit. Most mag drills have a +/- 1200 watt motor. Sorry for the conversions, I just took my bathroom scale and centered it under a piece of mild steel on my drill press. I couldn't find any data discussing the physics of annular drilling.