Cat6 has more insulation in the cable too. It has a plastic piece that separates the cable into 4 channels...one for each of the pairs. I'm assuming this is to prevent crosstalk.

It's a pain in the arse when it comes to putting the ends on the cables though, because you have to cut and peel back the sleeve, cut the plastic piece out, then push the sleeve back up so that when you put the connector on it has something to grab on to.

I think you can make longer runs with Cat6 than Cat5 too.