I imagine this will make me unpopular, but if you can't get used to playing 5's, what's wrong with sticking with a 4? About 10 years ago, I switched back to playing 4's after a 5 year period of playing nothing but a 5. I got pretty good on a 5 but never felt comfortable. And I've come to the conclusion that there is nothing I can do on a 5 that I can't do on a 4, save for 4 extra low notes, which other than a low D, are pretty much useless in my book.
As for this business about not having to make position jumps with a multi-string bass, I just don't get it. Well, I get the concept, but I don't get why it bothers people to make the jumps. Is it that difficult and painstaking that you need a neck the size of a baseball bat with more strings? I would think any gains by not jumping positions would be more than offset in the lack of playing ease.
Not trying to put those of you with 5's and 6's off by my opinion. I'm just saying that it's not necessary to play a 5 or 6 if you don't really want to. I've never been thrown off a gig for showing up with "only" a 4.