I have everything from a little Echo 35cc 3510 all the way to a 65cc Husky 365 with 28" bar. For clearing brush and small trees the little Echo is great. Anything bigger than 6" diamter on a regular basis and I'm grabbing the MS260, Echo 490 or Husky 359. If it were me and I needed a do-all smaller saw, I'd likely find a leftover or lightly used Echo 4910 for under $250 and run an 18-20" bar. These are older tech without stratocharging but are likley the lightest 50cc saw you wiill find. The mentioned Husky 543 would probably do it all for you but unless you find one one clearance or a good deal on the Redmax version they are overpriced as they are made by Zenoah. There's a clone version on Amazon I have been real tempted to get for $140 but I'm not certain if all the parts would interchange for future needs, plus Husky is abondoning the 543 and not sure how many parts would be available. Echo CS-400 is another great saw but getting close to 50cc weight.
