take it from a guy who drills holes in metal for a living: step up 1/8" at a time when drilling big holes in metal, especially sheet metal
Yeah! The 1" hole, I did with a gold bit that wasn't a unibit, the 3/8" hole i did with a unibit that had 1/32 graduations ... and it was MUCH easier!
take it from a guy who manages people who drills holes in metal for a living: Get a mag drill. Just a tad bit overkill for sheet metal, But why the hell not add one of those bad boys to your tool inventory.