|Ethernet up to 100 Mbs second uses two pair. 1Gb Ethernet uses four pair. Cat5 cable has 4 pairs. |
Three pair wire is Cat3 and is only good for 10 Mbs and telephones
So if you want to restrict yourself to 10 Mbs you can. If you want 100 Mbs or more then you are going to have to use Cat5 cable.