Having played many fretlesses (fretli?), as well as having played around with many alternate tunings (including tuning my 4 string down a 4th), I'm not a fan of the low B on a fretless. My
recently finished purple beast is tuned down to DGCFBb (high 5 down a whole step), for a bunch of reasons, some of which may not apply to you, but could be good food for thought. YMMV.
I need to have good note definition in order to play in tune, and between the stretches needed to play on the 1st three 'frets' and the inherent mud that comes with a 5 string, I feel I'm slightly more likely to slip in my intonation. By myself it's not a big deal, but when playing with a loud drummer and/or guitar player, I have a harder time hearing the fundamental of the note (rather than the rumble & boom). I personally would rather not EQ to a more upper mid-rangey quack any more than I have to. My ideal tone is somewhere between Geddy Lee and James Jamerson, but it always changes depending on where & with whom I play.
I personally haven't ever
needed to go lower than D (having Eb is super handy, though), and I like to be able to play E at the second position (which I find easier to play than switching between open notes & fingered notes. I tend to like to play middle & upper range stuff when I noodle around, plus I like being able to play harmonic chords, so another higher string appeals to me more than the 5 notes below low E.
Since I'm not playing bass in a band right now, I might have to change this someday, but I'd probably just get a fretted 5 or down tuned 4.
Fun challenge: tune down to DGCF and relearn all your bands's songs. :headbang1:
I was in a band where there were 3 songs in dropped D, all others in standard. While the guitar players spent their time dividing their parts to not play all over each other, I learned new fingerings for all the songs and saw a big jump in my playing skills. :guitaristgif: