> 250Kt on Departure
Here (Lisbon, Portugal) is common to hear requests for "high speed climb" even for lighter aircrafts, mainly A320 family from Portuguese carrier but some times also from other companies but this has nothing to do with aircraft performance ...
However TAAG (DTA) B747's often request higher speed due height limitation.
When the request is due aircraft performance limitations ATC due expect that pilot normally advise tower before take-off clearance. This is also true when aircraft is unable to comply with any other SID restriction ...
Principle is "if unnable to comply advise ATC"
Eduardo Ascensão
Air Traffic Controller