According to Official Guinness Records,
The fastest speed on a gravity powered snow sled is 134.368 km/h (83.49 mph) and was achieved by Guy Martin (UK) on the set of Channel 4's "Speed with Guy Martin" in Grandvalira, Andorra, on 10 January 2014.
For a complete list of 2014 records, please visit 2014 Guinness Records in Andorra.