Confusion reigned briefly when a Foriegn Departure Controller failed to authorize a high speed climb for a heavy MD11 whose weight required a clean climb speed in excess of 250 KTS. Wake turbulence from a preceding departure and fatigue contributed to the flight crew's ability to resolve the problem in a timely fashion.

Narrative

Before departure; I remember the Captain briefing to ask for high speed climb because the minimum clean airspeed for our weight was 278. On departure as we were accelerating and cleaning up the Captain said 'slats retract; after takeoff checklist; request high speed. The First Officer then requested high speed climb and Departure replied 'standby'. A few seconds later departure asked us to 'say airspeed'. We were at 274 KTS passing through about 6;000 MSL. The First Officer replied 'slowing to 250'. Departure then immediately replied 'high speed approved.'We were in light to moderate turbulence; I believe; from the A330 that took off less than two minutes ahead of us. I believe the attention focused on handling the aircraft in the wake turbulence of the preceding aircraft and fatigue were both factors. I believe fatigue was a factor because the Captain said he was tired. This pairing is a tough pairing; rest wise. This was the second leg of a long day and we had several long duty days starting with the first day of this pairing' This pairing requires you to fly long legs; many two leg days; across time zones requiring you to have to sleep during the day many times (the noisiest part of the day in most any hotel).