I owned both a 50 and 51 since 1987 . And severed me very well. I bought the 550 last year I had a learning curve. The idle on a auto tune I can not match. Always perfect I did have a little trouble with hot starts . I got that figure out. What I got is a saw that starts very easy and runs very good the sound is not bad. I will say this I will not do muffler mods to wake it up. I ran dirt bikes lawnmower. What I got a lot more noise and less power. My golf would not run with out the air filter box . Most small engines their air flow at speed not volume makes them run right. I know some people are very good and smash a muffler and get gains. The average Joe will say it is Lounder must be making more power. The only way to believe more noise is power is put them a dynameter. I rode small dirt bike a long time I heard take the baffles out for more power. What I got was loud and untuned a lot less. I really like a stock saw a lot less noise. If I need more I can get a 372 or a394 I will never expect a 394 to be a brush saw. To rip the guts out the muffler on the 550 and expect to run like a 394 . I think will not happen in my lifetime. Sorry duds hate me loud is not power.