A 30mm hole cut with a decent hole saw like Sutton through 6mm plate tales about a minute and a half if you drill a clearance hole first Norm.
Mark the hole with the hole saw then drill a 10 mm hole or bigger on the edge of the circle this will remove the swarf ,I also use an oil can for cooling and Lubrication.
You can use this method to drill through 2 inch thick steel .I usually use an old Sher 2 speed drill set on slow speed with a 1/2 inch chuck.
