I've got that same Cortland Sink Tip kit and if I were to cast all 12' on my 5wt, it would probably snap in half. Keep in mind I'm talking about my trout and bluegill weight rods here, smallies or LMB rods certainly could handle some more. But 8feet was barely manageable and in retrospect, really wasn't manageable at all although I "got away with it". I think starting at 4' is very reasonable and will give you an oppurtunity to think about how 2x that weight will perform for you.