I had the same predicament, and I'm sure many more!
I'm looking into the 2017. They both have the same appearance. There's many comparisons threads around, I read the most of them.
I still haven't got either bike, but in my mind, and when the dealer gets me one, I settled for the 650. Once I dropped my macho card and got over the more horse power "Oh oh oh" (Tim the tool man Taylor laugh) I thought that a 650 is plenty good. The style of bike doesn't scream speed, and unless you're planning to load the bike with an extra 200 pounds (pillion and gear) 650 should be enough for me to drag me around.