I've used a lot (about half way thru my 2nd 8 Lb jug)of HS6 in a 475 Linebaugh for loads in the 1,100 to 1,200 fps range. In that application it is superb -- consistent, accurate, clean burning and relatively economical.
I tried it in normal pressure .45 Colt loads and it didn't work all that well for me. Truth be told, I really didn't give it much of a chance -- more powder than I really wanted to burn for the high volume plinking loads I was going to use it in.
Personally, I'd stick with WW231 or HP38 or something in that burn rate for standard 38 special and 45 ACP loads. With HS6, you'll use 1.5 to 2 times as much powder to get basically the same results. I might reconsider for specialty loads (like gun 4 fun mentioned above).
Now with that said, if HS6 is available and the others aren't, I would would gladly use it.
FWIW,
Paul