CAT6 cable has a star-shaped plastic insert in the cable to separate the pairs. You need to use CAT6 rated jacks, of course. We got a chance to play with some of this in our cable certification class... CAT6 was very touchy, if you didn't make your terminations just right it wouldn't pass. There's getting to be less justification to go to CAT6 or 7 these days... the cost of fiber has dropped to where it's not much more expensive, and has many times the headroom.