I also have a Lowepro Slingshot 200AW. It carries my 20d, 17-85 (usually mounted) 50mm 1.8, 70-300 IS, and a 580EX flash, plus several accessories. It's a joy to use - just as advertised. It's very easy to move around to the front to get the camera out. You could probably do a lens change while standing if you were feeling saucy, but I don't feel that lucky.
It's comfortable to wear for a few hours, though with it loaded, my shoulder got tired after about 2 hours lugging it around. Maybe I'm a wimp?