I have a 7 string Conklin Groove tools lefty. I tune it like a guitar E to E, but with a low B. If I had a 6 string I 'd tune it E to E, like a guitar. I suppose this is becuase I have been playing guitar for as long as I have been playing bass, ....but it certainly doesn't forceme tothink differently that much.
So far I have stayed off 5 strings but have thought that if I play a 5 I'd tune it E to G with a top B. I don't really have use for notes lower than low E in what I do, except for the occasional Eb or D, though in the trio context with piano and drums, I can do some chordal things in shapes I already instinctively know. I suppose this does not work for the people who need the low B string more than I do.