Originally Posted by
Johnny F@rt Pants
FL320 is lower that normal for a 300, but not hugely so, however this will impact on the cruise speed.
In addition to this there is a marked difference in the cruise speed between a 737-300 and an Airbus, typically the 300 will cruise at about M.73 whereas the Airbus will be at about M.78, all of which over the course of close to 3 hours will make a difference. Add in to that the difference in the wind between FL320 and FL360 or 380 where the Airbus would probably be will all go to make up some time.
As to why FL320 was attained I can only guess, however it's usually due to ATC and the availability of higher levels, for example today I operated back fro Gerona, the flight plan was filed at FL380 however we only managed FL340 due to other traffic above us.