I've said many times, if I was going to put another bike in the garage it would be a 600.
That's the perfect weight and power range for the roads in North Georgia I like the best.
I think you made a great call there, even a 750 I felt would be just a tad big for the road.
My preference would be the Kawasaki of the three.
Good luck and ride safe on whichever you choose.
Just my worthless opinion so here goes.....
I'm going agree with Lazarus. Pick the Honda or go for Gixxer 750.
600's are a blast, light nimble but kinda anemic. They can be pushed for a bit more punch, but a 750 already has more to start with.