General comments re: all of the above
(1) I went to skinny booms after lots of wrist problems and forearm muscle pain (no smart arse remarks needed

) and have never ever even considered normal booms again. They rock.
(2) cheap carbon is not as strong as a good alloy like the ergal that Tecnolimits use, or the thick wall that Hydrodynamix use. The Tecnolimitz King custom wave boom at $470 (Jordo's one) is surely stronger than a cheapo $700-800 carbon. But, once you pay top $$$ for carbon they are way stiffer and MAYBE a bit stronger. Bear in mind, carbon is NOT designed for a large number of cycles (ie bend, straighten, bend, straighten etc). Thus they may be hot stuff when new but will fatigue just as much as ally. Well I have got 3-4 years out of all my mid priced ally booms in heavy wave use...and all of those were not busted but rather replaced by choice 'just in case'. 3 of the ally booms equals 10 years and $1000. Even better all of them are now spares in case I break a boom. Will you get 10 years of heavy wave use out of a good carbon? I doubt it. Thus I think cost IN THE LONG RUN favours alloy. On the USA forums I see questions all the time about how to replace the head on a Fiberspar carbon boom. Hmmm...
The only justification for carbon is the increased stiffness is good for large sails, maybe 7.5 and above.
If you can tell the difference between the 'feel' of a 4.5m wave sail on carbon vs ally, whilst your butt valve is tightening as you tear up a big wave, then you go for it. I doubt anyone can.
(3) one piece does no refer to the head assembly (jordo and Leech) it refers to if the tube is a continuous curve all the way around. That is, a good boom has only 2 pieces of tube in it, one big U shape with the head, and one big U shape that is the tail peiece/ extn tubes.
(4) no need to start a flame war BUUTTTTT........ in previous threads re: Neil Pryde durability a few people mentioned their NP ally booms broke really early and they won't buy NP booms again. They did say the warranty was good, but that doesn't help you if you drown on the 2km swim home from an offshore reef break...
In short, for wave use I'll always go quality ally (yes, even if I win 30mil in powerball this week) and if into lite wind freeride / race I'd use carbon.