Cat-5 / Cat-6

So I was at OfficeMax today looking for a network card and a RJ-75 wire. The cheapest they have is $14.99, so I decided to hold off on that. Now, when I went looking for the wire, there’s two kinds. Cat-5 and Cat-6 and something in between. I asked the guy, he tells me I need a Cat-6 for a 1Mbit connection. The line was much more expensive than Cat 5 so I didn’t buy it. Anyone know the difference? Apparently, they say 6 is faster than 5.