If you know your swingspeed please include it? And maybe what kind of sticks you use with 6.5?
I haven't but I would guess it would slightly lower ball flight and spin.
What is your swing speed? How high do you hit it?
I believe that i just half a flex stronger. So yea, slightly lower ball flight (SLIGHTLY), probably slightly heavier, and slightly less spin.
Distance, depends on your swing and contact. Going from 6.0 to 6.5 you wont probably see much difference. If 6.0 is really at the end range of your ability to load the shaft you might see a drop off, or you might see an increase.
Try out the KBS C-Taper. A little more stout than the KBS tour