I consistently move between a 19mm 4 string Precision and a 17.5mm 5 string Fodera, and that seems like an easy move to me.
I don't think I'd make too much fuss over string spacing, I accept an old Precision as 19mm, and my 5 as 17.5mm, that makes them the instrument that they are, why I play them
I've also had 19mm 5 strings and have an 18mm 5 string too, everything has been comfortable after a little while.
My only excretion to that was an ACG 5 I had, set to 16mm and that was toooo thin for me, was adjustable probably to 17mm or so, but sold before I changed it.
The Scott Devine Overwater Jazz 4 string is 16.5mm and that just looks weird, bet it's fast though!
So, I wouldn't get caught up in string spacing (no pun intended), try a bunch of basses, buy the one that is most comfortable.
Si