Thomas - every spring I thin my stands of young Ponderosa pines. Usually around 900 small trees. They are 6" in diameter or less on the base. I used my larger Stihl chain saw( MS270 ) with a 20" bar. I found that this situation became dangerous. As the day progressed, I would tire. My arms droop. Finally, the tip of the chain saw would make contact with my boots. A REALLY bad situation.
Now I do the same job with my new, lighter, shorter Stihl MS192 and a 12 inch bar. Cuts just as fast, I might have to bend over a tad more, my toes are now in the "safe zone".
Santa DID bring new toys. I bought a couple new chains for the 192. AND my son has decided that the spring project - identify, cut, drag, pile, chip - is not such a bad job after all. He has helped the old man the last two years. Still, dragging & piling is a PITS of a job.