Pete Seeger included a fishing line weight gauge:banjo string conversion table in his How to Play the Five String Banjo. I don't have a copy handy, but now you've at least got the reference. He also warned that the problem in using nylon fishing line as banjo strings is that the line takes FOREVER to stretch out, which is my experience too. So unless you're ready to retune in mid-tune, and then retune again when you reach the next chorus, I would suggest that you stick with the already referenced commercial alternatives.