Looking at WearyBizTraveller's spreadsheet, a DONE4 ex-GIB would be $6100, compared to $9200 for an ex-USA DONE5. You'd have to factor in your cost to get to GIB in the first place (closest intl airport would be MAD) and the cost of getting home (maybe from London and just 'chuck away' the final LON-GIB coupon) and then determine whether that saving is worthwhile, i'd imagine you'll save a minimum of $1500 - providing you fly economy USA-MAD/LON and back again (you can always use miles to fly home, or even to MAD if you have enough already). $1500 for me personally would be a worthwhile saving.

In terms of how this would leave you for the EZE-jfk-HKG leg, i'm not 100% sure of the transit rules so someone else would need to clarify that for you...I'd imagine that not having North America on your ticket would wipe that option out and instead you'd need to be going SCL-AKL/SYD.

Points to note; LPB-SCL is a Y only service, so not the best use of your ticket, best to splash $150 or so to get from LPB-LIM with LanPeru and then fly from LIM-SCL in J.

With your ATH/DBV flights i'd look at changing them to LGW-DBV//ATH-LHR or vice versa, DBV & ATH are less than 500 miles apart and i'm sure there's a train/bus service that would allow you to get to Athens easily enough. Failing that there should be pretty cheap flights between the two of them.

Also, with regards to your Oz Transcon if you can, get on one of the 767/332 flights, as they'll be far more spacious, i flew MEL-DRW on a 734 and whilst it was a very pleasant flight it felt very, very cramped after being in there for close to 4 hours!

The choice of carrier for intercontinental flights will come down to personal preference and it's certainly worth trying out as many as you can. I'd imagine you'll find big difference between some airlines, particually between AA and the other partners when it comes down to seating.

Personally, my preference is BA for overnight flights and QF/CX for daytime flights. BA has the advantage of having a true flatbed which I find I can easily get 8 hours of uninterrupted sleep on when I flew LHR-NRT, the angled seats just don't yield as much sleep for me, and i'm the kind of person who can (and will) sleep just about anywhere - I flew QF SYD-lax-JFK, and had plenty of power naps, but couldn't get to sleep properly just 2 or 3 hours at a time max.

QF/CX win it on daytime flights for what has been consistently better service on flights that i've been on, better catering and of course AVOD - albeit QF's is a bit hit and miss.

I'm not too sure whether you're timing your trip to co-incide with preferable seasons or not as you don't mention a departure time but a routing something along the lines of;

GIB-LHR-EZE-GRU-LIM-(LPB-LIM)SCL-SYD-PER-ADL//MEL-AKL-SYD-PEK-HKG-DPS-HKG-SIN-LHR-ATH//DBV-LGW-GIB.

Of course you could take out flights as you need in order to free up the chance to travel overland between them. The itinerary above is 19 segments, with 1 spare in South America and 1 spare in Europe that you could use as a final segment.

Finally, regarding NZ are you just going to AKL or are you going to travel around? If the latter, then why not look at doing a open-jaw and say, flying into AKL from MEL and then fly CHC/ZQN-SYD?