Clutching has major effect on the speed of the sled. If a sled is clutched correctly the sled will give more bottom and top speed than a stock clutch. If the clutch is worn you can drop speed very quickly. So yes it does.
he is asking if playing with the clutch will effect the actuall reading of the speedo, much like taking the stock size tires off of your truck and putting big mofos on. In the case of the sled speedo it wont make the reading any less accurate then is was when the sled cam fromthe factory cause the speedo gets its reading from the drive axle of the machine