How are you liking the new saw?
I've probably run between 50-75 tanks through the MS261cm (with M-tronic - computer tuned carb). Almost run through a chain (with a little usage that I've put on the second chain, we can probably call it 1 full chain).
It has run like a dream. It takes a few extra pulls to start when it is cold - not what I'd expect out of a new saw. But with the decompression valve pushed, it is very easy to pull, so not a big deal.
I had a project felling all red maple smaller than 12" DBH in a 50 acre woods. Thousands of trees - just dropped, not cleaned up. We'd switch off who was using which saw on different days or after lunch, etc... The other saws we were running were Husqvarna 359 and 455 that also run great. Both with 18" bars... On those 10-12" trees, the 359 was the best, while the MS216 and 455 cut about equal. Anything smaller, they all cut equal. However after carrying the saw for a few hours, the Stihl felt like it weighed 10 pounds less, so I'd run the 261 all day on the days it was just me. I know 1.5-2# isn't much, but it does matter!
359: rated for 3.9HP, 12.1 lbs
455: rated for 3.5HP, 13.2 lbs
261: rated for 4.0HP, 10.8 lbs (also had 16" in stead of 18" bar, so maybe a couple ounces less there too)
I haven't run a Husqvarna 550XP, so I can't say it is better or not...but I'm happy with this MS261. My one complaint (and I know I'm not the only one), is the fuel/oil caps. I'd rather just screw-on caps. Twice, I thought the oil cap was on and it wasn't. Now I know what to watch for...it is a slightly different feel when it is a "false clilck" vs. when it really locks down.