For speed, on geffy go down at red base, trying to catch the 4th nav in the way vinci suggests, and while it takes practice a sub 57-second time is easily possible using this route, or indeed faster.
ON ice fields, the bottom is slightly faster if you get it right, but strategically you would probably spend most of your tiem on ice fields going over the bridge.
The fastest times are usually only possible if you go into a server on your own and practice, since in a competitive race speed isn't everything. A good lap time on an Ice fields race, for example, is usually closer to 85/ 90/ 95 seconds since you don't do the bridge jump.