I have a Shaver HD-8 driver, and love it..!! If you get one, definitely get the hydraulic tilt, you'll thank yourself.
I drove posts by myself back in '12. A lot of trips on & off the tractor, but sure beat tamping in that many posts by hand. I did it through the winter when the ground was damp, it makes a world of difference. I used 5" for line posts,and 6" for corners. 6 incher's went in a little slower, driving them in 4'. But rock solid when you're done.
Don't sharpen posts, because if they hit a rock, and start of sideways, after getting down 2' or so, there is no way you can bring it back to plumb.
It would have gone a lot faster to have a driver, and get lined up to drive,as I'm pretty particular about how straight it is. I carried a small torpedo level in my pocket to keep the posts plumb both ways. With the hydraulic tilt, you can get them back in plumb pretty easy, just check it often, if it looks like it's starting to drive crooked.