I always get confused about the exact specification of these cables, so here is a detailed overview of them. I have had more involvement with this, because we are putting a new phone system at work, and we have different standard cables going through the office.
Cat 5 is older, but still good.Most implementations of this wire have a max throughput of 100 Mbps. Most peoples internet lines are not faster than this, so the chances of it impacting normal performance is low. Like all the cables listed here it includes 8 wires twisted wires in pairs.
A bump up from the Cat5. It runs on a 100MHz spectrum exactly like the Cat5, but it can achieve higher speeds due to the reduction of crosstalk, by tighter twists in the wires. I did not find any physics explanations of why this would be, but I assume that there is a magnetic field produced by the current flowing through the wire, that can cause current through the other wires, with the direction of the magnetic field dictated by the Right Hand Rule. One of the funnier things during physics tests was to see people randomly stare at their hand and curl their fingers, so they could figure out which way the magnetic field is oriented. Anyway, I assume by twisting the wires more, it changes the placement of the magnetic fields in respect to the other wires. I did not spend a lot of time researching, so that is a wild guess. Cat5e cables can reach gigabit connections or 1000Mbps.
We have this in our office. It runs on a 250MHz spectrum, and does more things to reduce crosstalk, not sure what those are. Anyway it can support 10 gigabit connections. At this point though, we are getting in to the area where the bottleneck of your connection may be your computer itself. Hard drives and CPU’s may limit what you can do with this kind of connection.
POE (Power Over Ethernet)
This means that a switch can send power over the cable for a device to use without connecting to the outlet. All the cables above support this, really what enables this is a more expensive switch. The only device I have seen that use this though, is our new voip phones. Which is nice, and most of our big switches were already POE.
So gigabit is a buzzword right now, which just means an 1000Mbps connection. It must be remembered though that all the pieces down the whole line need to be gigabit capable. From the switch, to the cables, to the network card on the PC. If you want a gigabit connection to the internet, your router needs to be gigabit, and you will need to pay a ton of money a month to get a pipe like that to your location.