John Pearse makes excellent weissenborn specific string sets
Something with a 60 on the low end and mid-upper teens on the treble side will drive the top good.
http://www.juststrings.com/jps-3160l.html
I play in D and G and C on a baritone Weiss
if you go C6, you must get much lighter strings
Open C is more for a baritone weiss