I have used my rotabroaches to cut 9/16" holes in 1/4" steel plate. They advertise for up to 1/2" plate. They work much better than twist drills for drilling holes.
Doing many holes ^^^^ this is the faster answer.
These are my first choice on any holes over 3/8" diameter and I have used them since they where introduced about 15 years ago.
I will add a twist -- I usually drill a small pilot hole just smaller that the center pin of the Rotabroach. Use that to keep you centered for starting AND it your work is thicker than the RB will cut completely through, you can switch side a cut from the other side to finish the hole.
On the regular tool-truck sold kits (1/4 to 3/4 dia.) You can also grind back the end of the end of the arbor to take full advantage of the depth of the RB cutter, many of which can cut though 3/8"s in one pass once the arbor is shortened. I have never seen the kits they say will go through 1/2" in a single pass on any of the tool truck - but I'm sure you could order it online somewhere.
