I would use mando cello strings, though with the shorter scale (not all that much shorter), it would have less tension. I thought people changed strings for Irish tuning? At least one place I was looking at tenor banjos mentioned different strings for the Irish tuning. I had a neighbor ask about the possibility of making a bass banjo. He had tried a heavy string on his banjo and said it sounded "interesting" and would probably be a good bass for porch picking. I thought he was nuts but I searched around and found that Goldtone. The user reviews are pretty consistant; it sounds okay but is uncomfortable to play (13" head). I would love to have an acoustic 4 string 5ths tuned instrument that plays down at or below guitar E. The real answer is to practice my guitar more, but for some reason the guitar just doesn't grab me like it used to.
"First you master your instrument, then you master the music, then you forget about all that ... and just play"
Charlie "Bird" Parker