Take this for what it's worth, but from what I've gleaned... #3 has small shaft internals and a deep lower, #3A is like the 3 but with bigger internals. #4 is sort of like a shortly #3 and a #5 is like a shortly 3A. That's what I got from reading through some stuff and talking to people. Whether it's right or not, I can't really say. I have been fantasing about putting a speedmaster on the boat. I believe Tunnel Vision ran a #4 on a box and Daredevil Scott happend to have one for sale I think (might have been a #5) so it kinda fit...
And there's your overly described internal monolouge for the day. :sifone: