To answer your question:
I have matching $400 fretted and fretless 5s. Not
status instruments - just well built, quality basses. Active 3-band EQ and 34-inch scale, they're a good test bed for what's possible at this price point or higher. Mine arrived with nickel roundwound strings and the B was
awful. Just mud - I couldn't determine the pitch most of the time, whether open or fretted.
I replaced the strings on both with
D'Addario Black Nylon Tapewounds and now both B strings are
GOOD. And for the record, that's ONE
PHAT B STRING at .135". Had to open up the width of the B-string nut slot slightly just to mount it. So I'm not sure a
lighter gauge string is the answer to improving B-string tone...
Regarding the tone/timbre when fretting above 5th fret: I think it's not worth considering unless you're a
SOLO bass artist. I've read concerns by others about how open strings sound different from fretted strings, and how fretting in the upper positions sounds less defined than in the lower positions. I agree that these phenomena
do occur, BUT...I think they don't deserve such concern.
I consider the bass to be a (very important) part of
the rhythm section, and as such, the sound it makes is heard
in combination with percussion and whatever other sources occupy the mix at the same time. Thinking of the bass in this way frees me to do whatever works--anywhere from nut to bridge--limited only by the character of my particular instrument (and my level of skill

).
I returned to music recently, and effectively started from scratch. I researched 5-string philosophy and bought two 5-string basses because I saw a clear advantage to having access to desired low notes
at the current playing position - without having to "jump to the nut" all the time. SIX MONTHS LATER, I'M SURE 5-STRINGS WAS THE RIGHT CHOICE.
4 strings aren't enough. 6 are too many, and going higher than a G string takes you into
guitar territory. Avoid muddled, confusing mixes by keeping instruments in their own unique pitch/tonal ranges (as much as possible

)
GET THE 5.
Put in the time and effort to learn FLOATING THUMB technique. 5 strings requires a serious approach to muting.
Don't look back. 