95% of the time the 650 has sufficient power / torque for me when two up with luggage. Probably has plenty of power 99% for my favourite pillion. For the rider, the other 5% happens when trying to out drag a powerful car going up a fairly steep hill.
On the motorway cruising at a GPS 80mph you get nowhere near the easy 60mpg on main / back roads, but the 650 will do it without protest, even if it's a little buzzy.
Above based on about 10 000 miles two up, much with luggage on, going down through Croatia and the south of France so a fair few alpine passess included. I'm on my second 650, but the 1000 is looking tempting as it will have the extra power / torque for the other 5% of the time, and has much longer service intervals. But the big question is, is the 1000 bike worth the extra 50% on top of a 650's price to me?