Hi!!!
Qantas does have a maximum of 183cm which i am right on. There have recently been though a couple people who are 184 etc who have just come online, they must be very good at hiding the bend in their knees or the person checking just didn't do a good job? The reason i believe there is a maximum with QF is that on certain 737's there are tv monitors located above the aisle and therefore would be a saftey hazard if you were any taller. I am 183 cm and i can walk underneath them but they still just skim the top of my head. If you were any taller it would be uncomfortable to have to bend each time you go under a monitor. Still definately go for it though!!!!!!!! as you said i don't know how long it would take you to get into long haul, maybe 50 years who knows!!!
Good luck anyway!
Oz