I've flown to Japan and Thailand (both ~10hrs from MEL) in economy on Jetstar's 787-8 with its 17" (43.2cm) seat width and 30" (76.2cm) pitch, no problems and I'm >6' (>183cm) too, with a little bit of baggage on me.
I've also flown on Scoot's 787 product which is very similar to Jetstar's - same thing, no problems or complaints either.
I'd imagine with the QF 787s with its slightly wider seats (17.2" / 43.7cm) and slightly longer pitch (32" / 81.3cm), this shouldn't be too much of an issue either?
I know it's budget vs non-budget, but I could hazard to say that the majority of members here have flown in (or perhaps are too used to) business class and therefore maybe have unrealistic / skewed expectations of economy?
I understand that everyone wants a nicer seat - this is a given, but it is economy and the expectations should be adjusted accordingly.
It's been a while since I travelled on a QF A380, but with the same pitch and slightly wider seat (by half an inch / 1.3cm) compared to the 787s, the only real difference should be the slight bit more horizontal space.