Nord, I am with you on the 4 nines, I would use that any day over the 3 nines since it is easy to get. Do you get tinnitus with .9999 silver? I got my 4 nines silver from the same place you mentioned and recommend them too. I bought 12g wire online and have enough for life. http://www.ccsilver.com/silver/superfines.html#four
Good luck on finding a small amount of commercially available 5 nines and don't hold your breath on the NJ source.
Cheers,
Ibis