I wonder if the flux-coated NS rod might be worth a try? It seems to be favored in industry — at least when I search for it, I get more hits for FC than bare. Being a finicky type about not having any burnt flux showing when done, I'd probably use paste flux too, with the FC rod supplying more as you go so you don't run "dry". I don't mean for normal bikeframe stuff, I mean more for like Duane's use-case, a thick SS part that takes a lot of heat.

I think I heard somewhere that the flux from the rod doesn't soak off in water, or not well. (Also true of some generic paste or powder flux like you'd get at the local welding shop.) I gather you're expected to hammer it off? Thinwall bike tubes don't like that treatment very much. (Finally, a use for the angry caveman smiley)

It's painful for me to watch when people use only the powder, heating the rod and sticking it in the can of powder to make it stick to the rod. But I guess long ago that was "the way".