there isnt any wind up that way this time of year. why bother?

There is no single answer to your question. Different airlines, countries and check in staff will mean no consistency in the baggage restrictions; even though you are travelling on a one world ticket. (some staff are casual contract that get a commission from excess baggage) The single big bag may be a problem, as you know they always seem to grow as you travel. If you are only taking a twin tip, you can do it. Borrow a big delsey or samsonite plastic wheeley bag. Pack your kites in vaccuum bags and shrink, putting all your kit in the case. Put you board in a single soft bag stripped of all bindings (its now a snowboard). If you're tight for room, leave the pump at home, they're cheap o/s & even cheaper to borrow. You end up with a big wheely around 20kg (which no-one will charge for under 20kg) and a small light board bag. The most you can get stung for is the few kg for the board, but the airlines you mentioned you will be ok excepting maybe BA, who have recently changed their baggage limits. Probably the biggest advantage, is this set-up is easy to handle and doesn't look like you're towing a box trailer when you check in. Good luck!

I've have always travelled QF/BA/AA or Virgin because they are so good with accepting my excess sporting baggage.
Virgin is not a problem anytime.
If its a RTW ticket you will have a baggage allowance of either 64kgs or 2 pieces at a max of 32kg per piece, with maximum length 277cm per piece.
I've never had a problem with QF as I give them a call and let them know that I am looking at purchasing a ticket with them but am travelling with sporting goods which I must carry. I tell them that Virgin have agreed to accept my additional or oversized baggage but I really like the service provided by QF/BA/AA. By the way measure your sporting bags before you call.
Everytime I have been told that it is fine for me to take my gear. Write down the name of the person, department, and location. If you are a QF FF get them to give you a reference # in your profile. I done this even when I have already booked. Then call them up when you book or with your booking number and tell them you spoke to such and such on this date and that they gave the OK before you purchased, get them to put a note into your booking that it has been pre arranged to carry your equipment along with the dimensions. Sometimes with my surfboard they tell me that I have to pay $50, but only had to pay it once on one sector with AA out of the BVI's. I had increased my equipment & I was so over on my allowance of 64kgs it was crazy so $50 was a bargain. Otherwise I've never parted with a cent at check in.
Posko had a great point about vacuum bags. Get the Large or XL one way valve bags from Kmart $9, that way you won't need a vacuum each time you pack. Just sit on it to get the air out. I've had mine for over 4 years now, they have done so many trips and they are still working.
I hope this helps.
Pm me if you have any other questions.

Took kite and board around and almost had a divorce over it! Meant we as a family had to reduce our luggage by 32 Kgs.........shoppers were not happy. All was resolved at the end though with myself being correct. Kite bag ended up being useful as it was easy to fit cheap African paintings and other crap.

Don't do it, there was no wind in N. America or Europe or Aftrica when I went. Got 1.5 hour in a "city" beach in N.Jersey (Sea Island City...check it)....memorable.

My total extra cost during the while excercise was US$180 )from LA to Chi, used Star Alliance). I did "tip" for storage in Dar Es Salaam and a dow ride to a remote island.........you can get a kit all around the world no problem, but lots of hassle if there is no wind...........don't do it...rent if you can at a kite beach.

I could have gotten lucky though, but have resigned myself to the thought that there is not wind much further from Perth. One wouldn't think even Perth is windy at the moment, dam troughs.