adding salt speeds up the reaction. not sure exactly why-I'm not a chemist, just the recipe I've used since high school.
I clean a lot of small bus bars, and I've always used the muriatic acid for a quick pickle, but the surface ain't pretty. There's absolutely no oxide or surface contaminates, but they're kinda odd looking. I'm lazy, so I want as little touch time as possible, but I want them pretty. I usually throw them in a vibrotumbler with cut steel rod and soapy water. Sometimes they come out amazing, and other times, it just sucks.
I still haven't arrived at the perfect formula, so I might give yours a try.