Just went to the local mower show. They had the new BR 550 on demo side by side with the BR 420. I don't remember the exact #'s but the 550 is about 40CFM higher and 12 mph faster. But the important thing was actually feeling the force. Much stronger. I am sure part of it is the concentrator tip. But the exit hole is the same size as the 420, just the tube is bigger. Weighs 2# more, but has much better ergonomics and has 4 isolator springs to reduce vibration. Sitting on the table the 420 bounced around while the 550 stayed in place. Same list price of $399.95. Quieter, bigger fan, half a horse more from the motor (4hp) Roughly 20% more fuel efficient. And it meets 2010 emmissions requirements. So it will be around for a while. Only downside for me is I have 2 new 420's. The other new one from Stihl is the 500. A low noise unit. $60 more expensive and more like a BR340 in performance. But if you have to have low noise, it is really quiet. He said a 600 is coming out in a few months. 4.5 hp a bigger fan than the 550 but he couldn't give any actual numbers yet.