Jazz: cba googling (need to get motivated to go to work), I think the major discriminator between cat 5/6 is the number of turns /inch in the twisted pair, and possibly also the screen coverage - but as you say, don't quote me on it. I've certainly got a reel of cat-5 in the shed that is solid core.
Doesn't cat 6 have a plastic filler as well to separate the 4 set of wires ?