I bought a Husqvarna 51 with a 16" bar as my first saw after the ice storm of 98. Used it for everything until I borrowed a larger saw from a friend about 10 years later when I was bucking up 8 cord of tree length hardwood. About then I started doing the mental math on how much of my life I had lost on the end of a smaller saw. I had looked at a 359xp, but by the time I got around to it, that saw was out of production and I ended up going with the 562xp with a 20" bar. It was a great saw and I did good with it for another 10 or so years. It was awesome for charging in to a big pile of tree length wood. not a lot heavier than my 51 really - mostly just the extra length and weight of the bar & chain. It eventually started to become a hard-start problem. I took it to a shop for a second opinion, and I got it - crank seals leading to crank bearings. The cost for parts & labor was going to be steep. According to the dealer, that saw (or any similar one that plugs in to a computer to be set up) may do this. Apparently the saw auto-corrected for the lean condition caused by leaking crank seals, up until it was too late? I ended up just shelving the saw and I bought an Echo 620P with a 20" bar on their "dealer days" promo for not much more than the rebuild would have been on the 562xp.
The Echo has been a fine saw, but make no mistake, it is not an equal to the 562XP, but it cost close to $200 less too. The 562xp is lighter, and turns a good bit faster - it just plain chews wood better. Eventually I will buy a short block for the 562xp and do as much as I can myself to put humpty dumpty back together again - minus the computer setup of course. As far as power per dollar though, that Echo is hard to beat right now.
Honestly though, the 51 is still my go-to saw for dropping smaller stuff and doing minor cleanup. it's light, compact, and dependable. I just picked up a Dewalt 12" saw since I have a dozen 20v batteries already. It is so convenient to just to be able to toss that in the truck or SxS on the off chance I may need to cut my way home in a storm, and not have to worry about fuel storage longevity.