Heya!
This is a bit tricky to reproduce, as it´s always dependent on the Cost Index chosen.
The initial 10000ft could very well also be because of the climb characteristics of the A310, as it usually reaches those 10000ft whithin 2-3 minutes after departure, leaving little time to accelerate as it is - especially if you factor in flap/slat retraction.
In my test flight i just did, i was at 300ish knots by around 18.000ft which seems about right I think 🙂