This question if so basic [to you all] that it probably belongs here. From what I understand as an aircraft climbs into thinner air, drag is reduced and higher airspeed results for the same thrust settings, the trade off is having to fly near 'q corner' I guess.

My question is: If you read the 763ER [did I say that right?-767-300ER?] specs and compare them to the A330 specs in wiki there is a small discrepancy in the 'cruising speed'. The A330 claims a 20km/h higher cruise speed at FL36 vs the 767 @ FL35. Would calculating cruise speed at the same FL for both aircraft close this 20km/h discrepancy?

Any links to useful reading or documentaries on this subject would be greatly appreciated.

Many thanks in advance, Jason