If you're going to be doing any quantity of firewood cutting, skip the 260 and 290 and go straight to the 361, at least. Life is short and having to stand around waiting for your saw to finish up with a cut is a waste of time.
I owned a 290 for years and recently sold it to my father-in-law, whose cutting needs are less frequent than mine. It was and is a fine saw, perfectly capable of cutting 20" hardwood all day long. For $340, it is a good value. But, as suggested, it is heavier than it needs to be and if you're going to be cutting any quantity of wood over any significant period of time, the extra weight will become an issue. The same applies to the Husqvarna 455, as well - they're great for the occasional user, but someone who cuts regularly will appreciate a pro-grade saw.
Though I don't have much time on a Husqvarna 359, I did use one a bit and I wasn't particularly impressed. It didn't feel like any more saw than my 290. I'm not sure how much more saw a 357 would be, and for the price I think I'd pass regardless.
The Dolmar products you should be looking at include the 5100s and the 6400-7900 series. The 540 and 510 are not enough saw to pull 20" with the kind of ease you are going to be pleased with, so don't even bother looking at them.
Also, the prices for the Dolmar saws you were quoted seem high. A 6400 should be closer to $475. If you figure that all your cutting can be handled with a 20" setup, a 5100s would be the best choice - it is very light, well balanced, and you should be able to get one for about $375. It is a heck of a nice little saw that can competently handle a 20" bar with .325 chain in hardwood. The 6400 is a very good saw, but falls victim to its weight - it weighs the same as a 7900 ($600 or so) but is 15cc down on displacement. That said, if you can get one at a good price it pretty much runs neck-and-neck with the 7900 in wood under 20".
You may also want to check around for a used 6400 in Makita clothes. HomeDepot liquidates their rental saws fairly regularly and they can be had for a very good price. The obvious disadvantage is that they're used, which can end up being a non-issue or a complete mess. Plus, there's no guarantee that your local HomeDepot will be liquidating one when you are in a buying mood, either.
I bought this saw from my local HomeDepot for a friend. Saw, a couple loops, and the bar: about $275.
And the 365 Husqvarnas that Baileys is selling for $499 are also worth looking at, as Steve suggested. Not a bad price for a powerful saw with a proven design. And there are Husqvarna dealers everywhere, online and brick-and-mortar, so parts should never be an issue. This saw may be your best choice for a serious saw.
Whatever you decide to do, make sure you find yourself a dealer who actually stocks the product he sells if you intend to buy from a brick-and-mortar retailer. In my experience, the guys who don't stock saws also don't stock parts and tend not to know anything about the saws they sell, either. Given the choice between working with this sort of person and buying online and handling the parts and service yourself, I'd pick online every time.