ode I have a set now with some extensions in and a few that don't.....I just paid attention to the head weight spread; shafts are Nipponn1150, grips and shafts were all within a gram. I ended up matching SW progression, grouped the clubs with extensions together and the ones without.
You are dealing with a constant weight shaft. Factor that in. Check balance points on each club it can be illuminating. I like Nippon because of constant weight.