I would go with the z400 for sure. I bought my girlfriend a 400ex and she rode it twice. It was to slow to keep up with us on the 450s. I just bought her a raptor 700 a couple of months ago. She loves it and I can also jump on it in the trails instead of the 450 and ride it hard and keep up. I dont no if the raptor700 is an option for you, but i strongly recommend that you look in to it. Very comfortable and fast, with fuel injection and reverse.