Thanks everyone for thier imput here!
Bob - Leadercalc is exactly what I was looking for. Can't beleive I hadn't stumbled across this before.
Juro - Thanks for your insights here and I look forward to seeing your own calculation progam - esp. for saltwater applications.
My main interest here is tying trout leaders for spring-creek type situations. Most of my fishing is 5x or finer and the composition can have a lot of bearing on your presentation, say during a sz. 22 bwo hatch. My frustration with the extruded leaders is that no matter what the manufacturers say, you can't have your cake and eat it too with prefab leaders. The turnover of a stiff butt section and the suppleness of a limp tippet section can not be acheived by a gradual taper of one material. This is especially apparent when fishing big dries or a hopper/dropper rig when it's windy.
While we're at it - has anyone experienced problems with blood-knotting floro to floro in finer diameters? This would be for the mid section of the leader of say a 6x leader. A surgeons knot will hold the connection for the tippet but I'm looking for the transfer of energy that can only be acheived by a blood knot.
Thanks again to all,