Since no response was given, posting this to let it disappear.
Quietest, oxy/acy or plasma. No, you can't cut with any accuracy with the gas torch, but it WILL melt the stuff apart. An old method of accurate cutting was to inject iron powder in the cutting port.
Cut-off wheel in a grinder. Noisy unless you dampen(weight) the sheet.
Sawzall with the right blade, noisy but quick, no sparks, a big + if you need a fire watch.