If you get 600 lumens from that light, even with 18650 or 26650, consider yourself lucky. That said, 600 lumens is plenty bright for city riding. And I'd agree that you don't need to worry about the weight unless you're riding in the TdF.

You should get about an hour on high, maybe a little more, with a 18650. If you use a lower setting you'll get more time. I use a 18650/2400mah with an XML-U2 light and get just over an hour, but usually I use it on strobe and get lots more than I've ever needed. I haven't done a long enough ride in the dark yet to test it. I carry a spare battery in any case and I have only used it when I didn't charge up the primary.