Some of you may have noticed, or thought it was a mistake when there were motherboards announced at computex 2017 with 5 gigabit ethernet, such as the ASRock X370 Pro Gaming AMD AM4 Motherboard (Amazon UK). This is because you "know" networking always goes in multiples of 10, such as 10/100/1000 and now 10GbE.
It turns out that it is actually possible to get 2.5 Gigabit networking speeds over the really old Cat5e cables, and even get 5 gigabit over the newer Cat6 cables that you might have. If you're unsure, check the sides of the cable. It will usually state on the side whether it is Cat5, Cat5e or Cat6. Don't get confused with Cat6A which is for 10 gig ethernet. This new standard is called IEEE802.3bz.
Unfortunately, I can't seem to find any "consumer grade" add-on NICs or switches (e.g. £200 or less) that support the new standard. I will keep my eyes peeled and post them here when I do (as well order/test some for my home). If you are a business and can justify the cost, then you can buy one of these off amazon. If you know of any PCI express addon cards or a cheap switch/router that provide such capability, please post it in the comments!
Depending on adoption and manufacturing, we might end up networking computers over thunderbolt 3 before this reaches the consumer level, or perhaps 10G cables/NICs might get cheap enough for us to skip this level.