Another good article:
Airbus A330-800 and -900neo, first analysis, part 3: performance | Leeham News and Comment
As I wrote before, the short range (2-3 hour) missions look to be the problem for NEO.
"Perhaps more interesting at this first analysis is the decline in fuel efficiency gain when shorter ranges are flown. We have a decline of 20%-30% from 4,000nm to 1,000nm. We can thereby conclude that Kiran Rao, Airbus EVP of Strategy and Marketing, meant something else with the quote “for 2-3 hour missions, the A330ceos are still more efficient than a neo,” (from this discussion with Aviation Week)."
So the sweet spot is medium range (aprroximately 4000nm or 8-9 hours. This is where NEO is most competitive with 787.
Long range? Forget about it... It's not an apples to apples comparison. The 787-8/9 are ultra long haul aircraft. The A330NEO is not. It's long haul at best. That's why the 787-10 is a more natural competitor. As a simple stretch which exchanges range for payload, it's missions are much more closely aligned with the A330NEO. The A359R is also part of the discussion, but unless -10 is eight across only I think it has a hard time competing against a lighter aircraft.