I had some standing dead trees cut down recently so I got a chance to use my timberjack. I found that the length of the handle is a little too short for much leverage, so I use a pipe as a cheater bar.
It lifts a 1' diameter log pretty easily.
On larger logs like this 1.5' diameter, I removed the jack leg and only used the hook. I couldn't roll it because it's about 60 feet long and in a bunch of brush. I could only rock the log back and forth in an attempt to "scoot" it up on to a 4x4.