I think wikipedia has all the tech details, but basically 6 has a faster rating and thus is capable of faster connections. That doesn't mean it will make your connection faster, just that it is less likely to be a chokepoint. Think of it as a water pipe for information, Cat5 is like a 3" pipe, but Cat 6 is like a 6" pipe (I'm sure I'm wrong on the proportionality of that comparison), so you can push more through, but only if your water pump (internet connection) has the ability to give you more. However, Cat5 does seem to cover the vast majority of speeds available. Cat6 I think is only useful for a gigabit network, ie computer to computer transfers, or if you got some really really fast internet that you're paying a ton for.