If the performance engineers have worked out that 220kts is the maximum speed you can fly without blowing out the turn and getting too close to the rocks, how can ATC take responsibility for the terrain separation? what criteria do they use and how is it different to what the performance guys calculate? Does ATC do any calculations at all? Genuine questions, I dont know what the answer is.
Because THAT calculation is based on the minimum rate of climb required for terrain clearance criteria. Obviously most aircraft climb at greater than minimum rate of climb and once high enough, the speed is irrelevant. As an extreme example, if you were 7000' 3 miles from PORPA do you think it would matter then?
Cancel speed restriction is clearance to cancel ALL speed restrictions issued by ATC which includes any speeds on charts. It does not cancel speed restrictions imposed by your Company SOP's. (250kts to MSA)