I started with the 550 in mid 2009. Have 2.5 years of loading with it (close to 40k rounds), I decided to get a 650 for the casefeeder and the extra station (might get a bullet feeder one day).
Love the 650, it's all it's cracked up to be. I love not having to take my hand of the handle to insert a new piece of brass... I can just keep cranking the handle.
I kept the 550, I have it dedicated to .45ACP. I may eventually sell it and just buy the conversion for the 650, but I like having the two presses setup, can just step up and load at either one.
Ron M. ('59 is my birth year)