Sven's quite correct.
The Sea King will fly at any speed with the gear down but there is a bit more drag. At light weights one does notice a lower nose down attitude for a given IAS.
It looks far better with the gear retracted.
Some guys in Devon found that the landing was little noisier with the wheels tucked away!
It will certainly go faster when on the water with the gear retracted!
Er...., don't ask!