'Constant thrust, variable noise'!
We did some LL at 300KIAS, but that meant that you couldn't use the standard technique for regaining ETA without exceeding the engine limits. It was also a rock-hard ride and any significant turns at 60º AoB bled speed off considerably. It used a LOT of fuel and the controls were quite heavy, particularly in roll.
Whereas 240KIAS at 250 ft was a much better regime - and gave greater time at LL.