I prefer to inform the pilots of the delays and if there are no separation issues, let them fly whatever speed they want. It''s their aeroplane and they know a hell of a lot more about flying it efficiently than I do. If there's no delay, most seem to prefer to maintain over 300Kts right up to the holding fix so that would suggest management are full of !!!!.
It wouldn't be the first time.
Let the pilots fly their planes - we'll keep them apart. It's that simple.