JC...in your description of the Castwell knot, you said you weren't sure how it would hold against big-game fish, I guess Marlin or something. Understandable.
But what about 10-15 pound Atlantic Salmon?
I tried the nail knot and lost my leader in a tree to knot failure, so I've put my faith in "The Castwell," I would just be incredibly dissapointed if I lost my first Atlantic because I put more stress on the knot than it was designed to hold.