I've had to cut some round and oddball shapes lately up to 3 1/2inches, I found that the Milwaukee metal cutting hole saws does great job with nice neat crisp edges. the saws are aggressive and don't need a lot of pressure to operate. I like these saws better as they don't walk around/vibrate and leave sharp edges that will cut thru the wiring grommets.
I also purchased a set of Milwaukee metal shears that also do a fantastic job.