Which Jacoby did you go for? I did consider trying out a v4 or v5 (probably the only carbon shaft I haven't tried on my Zen), though it is quite overpriced in this part of the world which put me off. No friends to test, and a no refund policy from the seller.
Tried Hayakawa, Cuetec, Kieth Andy, A Revo that was re-tapped, Triple60 standard and FG, and some Chinese/Vietnamese brands. Stand firm that Carbon is overpriced hype marketed at whoever will throuw money at it. Pros use what they get paid to use, and I am waiting to be proven otherwise.
Cuetec was the best for feel and sound, though the taper is horrible. The Kieth Andy a close second. Triple 60 was decidedly average, some no name brands out performed it in many aspects.
The Hayakawa KW shaft I have is decent, wouldn't have thought to buy one if I wasn't given it. Recently switched back to my Zen Xpro2 while I wait for a re-tip on the KW. Had forgotten what a beautiful piece of wood it was.