The fastest way I know of to drive a fence post into topsoil is to use the bucket of a front-end loader (most small farm tractors these days have them) and press the thing in. My neighbor built a 2000 ft. fence this way. Takes about five seconds per post in good soil conditions. But whoever is operating the bucket has to be very good at it, or the fence post is bent or goes in crooked. This is why I continue to use a driver even though my three year old Deere has a front-end loader. I have, however, used hydraulics to yank t-posts out along old fence lines. Much easier to take them out this way without damaging them than press them in.