I have't read through all 13 pages, but since there ARE 13 pages, I'll throw in my 2 cents.
First, chainsaws are not measured by their bar length. They are normally measured by their engine size in CC, but a better way to talk about them is by the HP they generate because a new 59cc pro saw will normally generate more HP than an older 62cc chainsaw. This is why so many people are recommending the Stihl 261. It generates appreciably more power than the previous 026 or MS260.
Second, what model of Husqvarna saw do you currently have? If you are happy with the way it cuts, and are only wanting to go up to 20 to have a little more reach, I'd just put a longer bar on what you have. The limiting factor on how long of a bar you can use on a saw is how much bar oil the saw can pump out. If your saw can oil an 18" bar, then most likely it can also oil a 20" bar.
Third, if you're looking for another saw because your saw just doesn't have enough power to cut the bigger stuff you're dealing with, then I wouldn't limit myself to something that normally runs a 20" bar. If you're running an 18" bar now, you most likely have a saw that's in the 45cc to 50cc range. IMHO, if you're cutting hardwood, those saws are best suited to cutting wood that's 10" and under. They can cut bigger stuff, but they are a lot slower when doing so. The 261 is a 50cc saw, but it puts out 4hp which is more in line with what you'd expect to get out of a 55cc machine. If you normally don't cut much that's over 12" across, it doesn't make sense to carry around the extra weight of a 60cc or 70cc saw. Most people in that situation opt for something in the 45-50cc range, and the 261 is definitely king of the hill in that category. If you cut a lot of stuff that's 18-24", you're better off with a 60cc machine. I still prefer a 18" bar on my 60cc saws because it keeps my bars and chains the same as what I use on my 50cc machines. People will say that it takes longer with a shorter bar because they end up having to make a cut from both sides of the tree/log. If I'm felling, I like the convenience of a longer bar, if I'm bucking, it doesn't make a difference. With an 18" bar on a 60cc machine, I can drop my depth gauges down to .030" or .035" to take advantage of the extra torque which allows me to cut noticeably faster than what I can with a 20" or 24" bar. If you know what you're doing, you can cut through a 24" diameter log with an 18" bar without cutting from both sides.
Lastly, if you're cutting very much that's over 20" across, I'd strongly recommend getting a machine that's 70cc or bigger. I own several saws, and I jump straight from 60cc with an 18" bar to 90cc with a 28" bar. 90cc machines are HEAVY. They aren't much fun to run, but if I'm spending much time in wood that's over 20", my 90cc saws will cut a LOT faster. A 70cc saw would do the same, but I sometimes need to run a long bar (36" or more on wood that's 4' - 6' across), and the 90cc machines run those better than a 70cc machine will. If I knew I would never need to run a bar longer than 32", I'd get a saw in the 70cc-76cc range and get a 24" and 32" bar for it and call it done. That setup combined with a good 50cc machine is a good 2 saw plan.
FWIW, I run Stihl saws and am brand loyal primarily because I have bars, chains, and spare parts for them. Adding a Husky or Echo would end up costing me a lot more than just the sticker price.
