I found myself in need to cut 1/2" mild steel plate today. The cut was about
4-3/4". I tried first with my only reciprocating saw which is 18V cordless and a Lenox 18 tpi blade (the only one I had on hand). The cut progressed very slowly. I thought I would try my Bosch 1590 jig-saw not expecting much (Bosch do not recommend use beyond 3/8") and I was not disappointed: It was even worse. In the end I did most of the cut using a hacksaw with 18 tpi blade (A DeWalt past its prime). This in fact was the fastest way and also the cleanest (except for the mess that the lubricating wax makes :-).I specifically avoided using a 4-1/2" cut-off wheel in my grinder: I find those things very messy and hard to control. This policy was vindicated when I tried to cut off a couple of the corners of the said plate. It was not that fast either.
Oddly enough I find using the hacksaw less fatiguing than any of the other tools: something about the better posture and rhythmic dynamic movement as opposed to having to hold a vibrating tool still.
Although I do not expect to have to cut this sort of material in future very often it got me thinking: Say one needed an even longer cut - 6" to 8". What would be a good low cost (