I really debated on both but ultimately decided on the 6100. They both run great but I liked the features on the 6100 more (fuel capacity and efficiency, weight, air filtration). The torque advantage of the 6400 really stands out on bigger stuff but for limbing and smaller diameter I would pick the 6100 every time. The 6400 may be heavy but its a runner and nothing to turn your nose up at. The 6100 feels like a 60cc class saw, which is a good thing. Now that I have a 7900 it doesnt matter lol. These two saws have made Dolmar my first choice and opened my eyes to the world outside Husqvarna and Stihl. The 7900 is like a sleeper saw because most dont know anything about them, which Ive had a lot of fun with so far.