TPE-HKG is so great route, but some arguments are still possible: Is it really a international one rather than domestic? Without Taiwan's limited destinations, will so many taiwanese fly to HKG to get flights to all over world? Besides, it's still the busiest, of course.
Some other route; In a case of SEL-NRT, it was proved to be 8th officially, but there is some irony. NW and UA operates both 1 and 2 daily 747 flights in this route to make use of their NRT hub, but Korean and Japanese liners cannot get more slots, actually their oppertunities are reduced for many years. In this route almost 10 daily flights, most by 747s, are operated, and seats are run out months ago. Even K-J govts negotiate to operate SEL-KIX-HND transfering route.
I bet the real winner to be London-New York, it cannot be judged by mere the fact of number.