Greg,
My recollection from Dr Gaddy was that the hot salts started a inter- or intra- granular reaction in the solder (the tin, I think) that progressed over a long period of time, causing it to fail the joint.
So, for a soft soldered sxs barrel set, don't use salt blue. But I have used hot salt blueing on a set of Spanish barrels that were, clearly, brazed.
There are many differences in the two processes and results. My experience seems to suggest that the rust blue holds up better. But that's just a feeling and I have never seen any real test information on that.
