Hello Fred, Yes-I play regular plectrum tuning CGBD for (4 string) plectrum, and same tuning for Irish tenor (capo on 2nd fret to put you in "D" the most commonly played key for Irish music, and pick over the B string). You can also use this tenor style to "flatpick" single string tunes like "Liberty" or "Dixie". The same C tuning for 5 string "Classical or Ragtime" and then G tuning DGBD,for 5 string bluegrass or old timey. One just has to rethink the chords, not too difficult, just set your mind to it. Most of you also play guitar or mandolin, and oyu need to rethink chords. One banjo-Plectrum banjo-Dixieland, American standards (Ain't She Sweet), Polka (this is a great venue). Singlestring Tenor style and Irish Banjo Classical/Ragtime Banjo Bluegrass banjo Old timey banjo
I used to think the four-string was the most versatile -- but that probably stemmed from being a mando player and a predilection for tuning in 5ths. I've recently begun playing my 5-string in plectrum tuning more, which gives me greater familiarity with the entire range of the fretboard -- something I've never been able to accomplish with non-symmetrical tuning schemas.
Still, I have to say that two banjos are essential, 5 and 4 -- unless of course, one is willing to drill an extra fifth-string rig like jon has.
4 string is definately more versitile. There are some like Bela who can really "think" the compexities of the instrument with the open drone, but those musicians could have been brain surgeons if they wanted too. I have found that the simplier the instrument (i.e. clawhammer "Cripple Creek" or a simple tune on Irish whistle), the more complex it is when you really need to improvise. I play highlandpipes, you have 9 notes and people have play with me, i can't just jump into a tune and "jam", it would be a disaster!! I can play what I hear in my head on 4 string and play a different phrasing the next time around, in any key (some better than others). I can "jam" on 5 string but often rely on memorized licks to get me through some changes. Try some old standards with 5 string C tuning "Carolina in the Morning" is fun with the decending bass note.