Cable: Cat5e or Cat6 ?

At present there is still some discussion whether new installations of cable should use Cat5e or Cat6. It is often incorrectly assumed that if Cat6 is run then the ability for a Gigabit Ethernet is available. In truth to attain a true Gigabit Ethernet speed, then all components of the network have to be rated for gigabit. Items such as switches, network interface cards and hubs also need to be gigabit rated. That doesn’t mean that there is no difference from Cat5e and Cat6; the difference between these two is in the transmission capabilities. Where it is known that Cat5e can support gigabit speed, Cat6 is actually certified to manage Gigabit Ethernet.

Also, the specifications on Cat6 is better suited for the environment that is usually filled with twisted pairing cables and areas that you generally find with lots of items that cause interference, such as electrical rooms, phone equipment rooms, power lines and lights. For most applications you will find that Cat5e is still acceptable and even preferable to Cat6 because it is less costly and still performs nearly as well. If however you know for sure that all of the components of your network are gigabit rated and the amount of data that will be transmitted will require that you have certified gigabit capabilities, then Cat6 would be the preferred choice.

Source:
Network Cabling Cat5 Vs Cat5e Vs Cat6
http://smbtechnologytoolkit.com/2010/network-cabling/