Its supposed to be quite a difference from what ive heard from people using the 6.5 parts for their old motor. For me, I didnt request to get that done or anything when I sent it in, so most likely they'll just replace it with the old version.
I only upgraded the rotor at this point--it fits fine in the old can--it's actually slightly smaller in diameter, but the magnets appeared to be stronger. When I can get the new endbell (with new bearings) I'll install that too.
I noticed an improvement in both torque and lower temps (motor & ESC). I actually had to gear up to take advantage of the new performance--it feels like a motor with a lower KV, but YMMV.
Oh and breaking--it's unreal compared to the old rotor. I've flipped my Revo forward on it's lid a number of times from the increased breaking ability.