For my two cents worth, have you heard the 4-string acoustic basses used anywhere? I've heard several in the past month, at the Uncle Dave Macon festival and Smithfield Fiddlers Jamboree. Not sure all the makes but one was a Fender. None really sounded good enough for me to want one. The uprights are huge but sound soooooo much better in an outdoor acoustic venue, which those two are. (No electrics allowed) A 5-string would have the same limitations as the 4-string outdoors.