I would like to ask how is with flexibility at this racquet. I was also looked to models 8000 and 9000 but I think that these racquet are more stiff than 6000 model is which means that is hard to play if you don't have strong arm. For advanced player is 6000 enought or not? I prefer mid flex racquet and models 8000 and 9000 are extra stiff. And of course there is also model 7000.