It will be cheap rolled mild steel, should cut a treat with a HSS (high speed steel) tool bit. If you go wait a min or so between each drill hole (if thats your plan, 80mm drill bits are err rare, biggest i've got is 10mm, lol.
I do have a 40mm arbor based piece though which made easy work of cutting my case a while back (still havent filed off the edge though lol). I'll post a pic'y later when i find my digicam.
Oh as for case airflow replacing those stock drilled mech bits with something less restrictive can reduce case temps alot. Mine went from 35-40c to 25-28c (
cpu temp dropped from 50c to 42c as well)