I bought my first six-string bass this summer after playing four-string basses exclusively for over 15 years. Honestly, I can't imagine going back to four (Ok, I could probably do with a five). Having the extended range of the B and, although to a lower degree, the C strings without losing what makes a four a four seems like a no brainer.
Why haven't you made the change to a six or even five string bass already?
I don't like those two superfluous strings. Don't want them, don't need them, don't like music that uses them (with a couple exceptions).