Couple of questions...
You are Spey casting for stripers correct? What type of line (sink/float/intermediate) and fly (hook size/design) do you want to use?
Sinking tips and lines really don't need any more than a few feet of leader. Not just the leader but the line design itself impacts the ability to cast up striper sized flies.
The Skagit systems are generally most capable of throwing big flies because these Spey lines concentrate the grains in a more stout, shorter section of line thus dissipating less energy for the sake of finesse like long belly lines.
The leader is an important thing to consider, but first think of the line type and fly, then the line system, then the rod to match the line system, then finally the leader.
Where / who did you take the lessons from?
IFFF Certified THCI @ 2005
Capeflyfisher Guide Service
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and Founder, Worldwide Flyfishing Forum