I have been here in EK 18 months, on the 330/340 fleet, (by the way life is good here!!) for me, upgrade will be on the A380 and I don't expect it for at least 6-7 years+ from now minimun, and if I am lucky.
Obviously the recrutment team would sell you 4-5 years, that was true, if you would have joined 4 years ago, but not anymore.
777 side, I think the same way, 6-7years+++, my friends on the 777 say that the upgrade will be quicker on the 777, but again not anymore!! There is lot of 777 orders but mainly for aircraft replacement!!!!
If you join now, yes you will become captain within a decame maximun but not 5 years!
Captain within 10 year, on a jumbo, on a major airline, it's still a very deal compare to other airlines.
Now, right seat in EK v/s left in QR (on A320), for me this not even discussion, I would never work in DOHA!! no way... The life style is too important to me. And I had the choose to....
Good luck.