No step drill for me. Only quality twist drill and a bit of oil or tranny fluid to help with cooling. 9mm that's 5/16 thick or close to that. I would use a 3/16 or 1/4 drill bit and chase out the hold with the correct size after. I feel the 3/16 or 1/4 bit has a bit more meat on the bit to keep it from wobbling under force. I know, I know, were are suppose to use the correct feed rate. Who does that?
Make a U with a couple sticks of lumber on a piece of plywood and mount a Destaco or hold down clamp to keep it from moving and holes will be super accurate. Oh, do clamp that plywood to the drill press table.