The neck on mine little different; it's a three-ply through-neck. There's a central mahogany strip of around 7/8" with laminates each side of that. To be honest, in a live context I don't hear much difference between any of my Thunderbirds, but would say that flat (ie when recording direct) the Gothic is a little fuller tonally...at the end of the day I kind of know what my desired tone is, so I'll just set everything on the bass to 10 and tweak my amplifier to achieve that sound.
Shucks, you're right, mine is three ply too (I just looked at it again), sorry for the confusion.
I believe the fullness comes from the pumped-up pups.
