On anything but a light B747, 250 kts on departure will require leaving it at Flap 1 or possibly flap 5), which is inefficient for fuel & noise. At LHR, the speed limit is max 250 or min clean (often about 270 in a B747).
On arrival, good gates are 250 at 10,000ft at 30 nm track, but fun can be had and 360kts at 2000ft with 20nm to run also works on a DOH-BAH shuttle
So, it all depends on whether or not you are allowed to 'do your own thing'
