When heavy on departure, I have generally found that ATC will accede to a request for (say) min clean + 10 kts contained in the readback, such as
"request departure climb 265kt, operational requirement". LHR SIDs actually contain the note:
Maximum 250KIAS below FL100 unless otherwise authorised. which invites such a request. I really can't recall any refusal on either this (UK) or the other side of the pond. In the rare occasions where manoeuvrability (eg radius of turn on LHR BUZAD3J/2K) requires a lesser speed, you should be planning a delay in flap retraction anyway.
It is clearly undesirable for a heavy jet to be climbing with flap extended for longer than necessary. Fuel and bank angle restrictions will be the obvious penalties otherwise.
JD
