I am totaly converted to rotabroach. Fairy near the size in diameter, can drill with less power and downward force is very low compared to normal spiral drills. Force needed to push the spiral drill is considerable, if I remember right, somewhere 200 kg range for 10 or 12 mm drill with nominal feed.
I have tried holesaws too, but they don't cut thick sections particulary well, without anciliary holes and some waffing about. Doable, but slow and pretty much allways you need something to finish that hole, unless you are welding it.