Realise it has been a while since you posted, but thought it might be worth responding and trying out this forum.
I have personally been looking at the 650 with some interest. I was however warned that it is somewhat underpowered. (But then the guy suggesting that had a 1600).
I was hoping to upgrade from a 535 and like the looks of the 650. But seems the 650 has slightly less power than a 535 so I have decided to stick with the 535 for now.
I would strongly suggest you go and take a test ride on one. Its the only way to figure out if it is suitable. I have done this and thought it felt like it had more than enough power. However my test ride was only short and around a couple of blocks twice. You really need to take it with your pillion and get it on a motorway up to 70mph to determine if you feel comfortable on it. Some places will allow you to take the bike for one day and give a full refund on return (if you pay in full). This should give more than enough time to test the bike and decide whether it works for you.
If like me you are just interested in cruising then this is more than enough power. Also important looking at comfort as I find the 535 tires me out quickly on long journeys but I love it for commuting.