I just got a 1050xt, didn’t consider the 650, but did consider the guzzi 85tt, which I really liked.
For me the smaller bike would be fine for 99% of my riding, but didn’t like the thought if thrashing a small engine on the rate occasions on tour when you want 100mph cruising for several hours. This, and simply not being ready for a little bike made the 1050xt an easy choice.
So far, over 50mpg, light supple handling, plenty of power, narrow for filtering, and imho looks great, a big part of ownership is aesthetics, and whilst undeniably subjective, the xt does it for me.
If you like the style of the 650 then it’s undoubtedly the sensible choice, but we don’t love bikes because they’re sensible