First and foremost, the user that adviced you to look at the connection speed is 100% right. If you establish a gigabit link with a gigabit device, it makes no sense to upgrade other than future proofing.
There's no point in going beyond Cat 6a. Keep in mind that the length of the cable is a big factor as well. For 1/2.5GbE, Cat 5e is plenty (for at least 100m). If you plan on going to 5/10GbE now or in the near future, Cat 6a will get you there with ease (for at least 100m). In both cases, keep the cable as close to the required length as possible + a 30cm/1ft service loop (slack) on each end. That will cause no more signal degradation then necessary and make for a clean install.
What you should be asking is whether the cables qre the bottleneck in your network or not.
Is there any link that is not negotiating 1Gbps? Do you have devices that could push 10Gbps but the cable is not allowing it? If not, then there's no need to upgrade them.
Unless, of course, if you want to do it just for fun, which is also a legitimate reason 😄
A 2 metre 5e cable will be a hell of a lot cheaper than a 2m CAT8 cable, and unless your internal network is faster than a gigabit or two there's really no point in using anything more expensivethatn 5e or maybe 6.
Cat5 and 5e are good for up to 2.5G. So if your hardware doesn’t go faster, there won’t be any improvements by changing the cables. (Well, unless you have a really wonky one.)
If it's actually Cat.5 then it may be worthwhile to look at replacing with something newer, but if you're on Cat.5e then unless you wanna start playing with 10Gbit you'll probably be fine.
If you do upgrade, you don't need to go to Cat.8 simply because it exists. Cat.6a or even plain Cat.6 will do everything you're gonna need in Gbit networks.
I have 3 ethernet cables together with a dozen power, audio, display cables. Would it be better if I have a separate bundle for them?
How would i check if they are shielded? They are around a meter long each.
You can guess if it is shielded or not by how hard the cables are to bend, but otherwise you need to cut them open and see if there is some metalized foil wrapped around the cables. I think this shielding is not mandatory by the specs so usually only the professional ones have it.
Some cat 5e cables are able to do up to 10gbps for short distances (less than 30 meters).
2.5gbps and even 5gbps should be achievable for most cat 5e cables.
Your cat 5 cables could be a bottleneck depending on their quality. If they are high quality they should be able to achieve 1gbps over short distances (30-35 meters).
However your router only has 1gbps so it doesn't make sense to upgrade your cables unless you also upgrade your router (and presumably your network cards).
If you decide to upgrade your networking I'd recommend that you buy cat 6a cables.
Cat 7 is only a standard recognized by ISO if I'm not mistaken so finding good cables is harder.
And cat 8 is the newest standard recognized by both ISO and IEEE, but it's too expensive for home users.