tws, you can make a furled leader out of just about any sort of material so the Fireline is a definite possibility. However the action of the leader is definitely determined by the material used to build it. How stiff is the Berkley stuff? What is the diameter? A basic taper of 10-8-6 is going to have 6 threads at the tippet end so 6 x 4lb test is a 24# test tippet end. A Fireline leader might be a bit too thick and stiff to use for delicate dry fly fishing. This is reason we use tying thread for dryfly leaders. A furled mono leader made from Fireline might work for bigger flies or for saltwater fishing.

Al