My #1 tip is hang on! Just kidding. It will be quite a different experience in my opinion. The obvious difference will be the ergonomics. The 650 has more of an upright position whereas the zx6r will have you more bent over. It might take some time for your body to adjust to the new riding position, but be patient... it will adjust. The power and handling will be the other big difference. Take it easy with her at first and she'll treat you just fine.