I played a 5-string German upright bass for a couple of years in the local university's orchestra before having my Alembic built. Roger Spencer, then a studio guy in L.A. on upright and electric, tried talking me into a 5-string electric (citing JJ), but I couldn't conceive ever needing that much bottom with an electric (and of course Chris Squire and JE got by just fine with 4 strings). 5 years later, I succumbed (after spending some quality time with a Chapman Stick) and had a 5-string Jazz Bass built, and tuned all my 4-strings down a 4th for about a decade. In 2002 I picked up a bargain Conklin 7-string, which I dubbed The Tendonitis Machine for what it did to my wrists when I played it for more than a couple sets. I found that I only really used the bottom 5 strings and the additional treble strings just made me do more mental gymnastics and play some interesting unintentional harmonic variations. Now, interestingly enough, I most enjoy playing 4-strings and only miss that 5th string occasionally. For me, I suppose it's a cycle of challenges that dictate what I enjoy. As much as I enjoy playing 4-strings, I can see at some point migrating to something different for the sake of migrating to something different.. Anybody remember the concept of tuning the bass in major thirds? It's a thought...
John