The 580 is more for heavy debris and has a waist belt. But yes, they are close in performance on that test and their indexes are very close too if you calculate them. The 580 has significantly higher cfm while the 570 has significantly higher mph, likely due largely to different nozzles on the ends. $50 to $80 shouldn't be much of a decision maker on what I consider to be a key piece of lawn care equipment that should give several years of service, in my opinion. My purchase of a 580 has all but eliminated my use of a wheel blower. I originally was considering the Shindaiwa EB802 because I have gotten such great service out of my EB630s, but the exhaust on it seems to make it much less of a blower than it should be. For me it came down to the Shin 802, Echo 770 and Husky 580 and the 580 untimately won.
Here's a short video I made of the 580 in action...should have put some bigger firewood out. http://www.youtube.com/watch?v=RgxwaIoSuhg
Here's one with me playing backetball with it. Try that with your Dolmar http://www.youtube.com/watch?v=oovm_FtUE6k