To touch briefly on things I've read on these saws:
The Dolmar 7300 is built on the same chassis as the 7900, (If I recall correctly) so in a word, you are buying the weight of the big saw but not the power. Take the step to the big saw and enjoy all the power you will ever want or need.
If you are looking for a low end 70cc saw, perhaps something smaller and lighter would be better suited for you...
I don't know if much has been said about the Husqy 570, other than its a little fat in the ass, but over all it runs good. I also believe its built on the same chassis as the 575, at least it specs at the same weight. You can spend another $90 for a half more horsepower... but thats up to you and maybe someone can shed some more light on how those two models stack up.
I think the Jonsered 2171 is the equivilent of the Husqy 372xp... if that is the case, its an awesome saw. It would produce around the same HP of the Husqy 575 and save you a few pounds. It would out perform the Husqy 570 and save you a few pounds. The Dolmar 7900 would smack all the aformentioned saws down and fell 5 trees with a backwards chain....
Okay, so some stuff I made up, but thats what I've kinda put together from reading some threads. maybe an expert will come lay down some real knowledge here shortly.