I came to five-strings in the mid-80's after they became available from regular manufacturers.
I never was comfortable on a four string as I'd begin a certain run in first position and invariably have to finish it up the neck way too often. With the five I can play a two-octave run across the fingerboard in the space of a few frets. I just see the fingerboard in a lot more linear fashion on a five. I would not go back to a four, don't even own one, wouldn't know what to do with one.
I think it's down to the player: I know guys that kill on a four, and I know guys that kill on a six or seven. By the same token we all know people that can't find their butt with both hands and a flashlight regardless of WHAT they're playing. I wish I could say sticking with a (your choice here) improves your playing, but I just can't. I look at learning on my chosen instrument to be no harder because of an extra string than I would to say it's easier if I had one less string. I double on keys, maybe that's it: I never think a 61-keys synth is somehow limited as it's not an 88-key piano. They're just different and good in their own ways.
I know lots of 'former' five or six string guys that are back on a Jazz and loving it. And if that's where their musical journey takes them, I couldn't be happier. But for me and my own trip, I got better, faster, on a five, as it just suited me better.
It's very easy to be hammered into playing 'what you're supposed to play' by friends and peers. Witness the endless 'where's the Fender?' stories. I get the occasional, 'Hey, you gotta take one string off that thing!' when I show up: Nobody EVER says it AFTER I play. Because, really, aside from the occasional low root C or D, if you don't see the axe and I'm fitting in perfectly in the charts, HOW would you know?
J o e y