I'm not sure whether it matters if the speed is 250kts(
) or,say, 280kts. The crucial thing is that the traffic is presented in the same manner in order to reduce bunching at the interfaces,be it to the next sector or unit. I recently watched an incident between 2 a/c on the same SID from the same airport,100 miles north of the departure field,similar types-and no,not an A340 involved, and they had an airmiss. Now if they had been flying the SID and a similar speed there is no way that the in-built airfield separation could have been eroded so much.
It seems that the airlines want a "pile'em high,sell 'em cheap" type of service nowadays and are interested purely in sector throughput and eradication of delays. This will require a major re-education amongst the ATC fraternity and will not be a painless experience. From an en-route point of view it is the bunching which causes the major problems so this has to be worth a try for at least a couple of months and people not giving it a fair chance will not help the validation of such a procedure.