I like my little 550xp. Still not sold on the auto yet. I think stihl mtronic are a little better in my opinion. But I like the 550 better than the stihl. Its light and slim. Easy to throw around. I run a 18" tsumara bar and 3/8" chain. Its cuts great.I'd go with the 261, I think you'll really notice that 3.3 lb difference.
I run a 550XP mkII which is Husqvarna's equivalent of the 261, I've got a 20" bar and 0.325 pitch chain. Works good for what I need it for. But it does have to work if the bar is buried.
Not sure if US dealers are the same, but the 261 is on sale in Canada right now for $50 less than the 391.