I would get the 600 over the 550.
As far as the Husky 580 goes, yes it's a very powerful unit and it easily outblows a BR600M. But it is a gigantic and heavy unit that I wouldn't recommned for the smaller guys out there....we're talking around 30 pounds fueled...big, heavy and loud as hell. It is pretty comfortable due to an excellent harness system. I love my 580 but just wanted to point out that some people might find it too much of a burden to use.