Selfhosted

Cat8 is pointless with gigabit equipment as far as speed goes. Cat6 will do 10gig, you just had bad cables.

Cat 5e

The fact that your old cable was cat5e has no bearing whatsoever on you getting shit speeds before changing cables. The gigabit spec was codified and products were on the market before the cat5e spec was ratified. Gigabit ethernet was literally made for standard cat5. I bet your previous cable was terminated incorrectly, and was only using two of the four pairs, limiting you to 100mbit.

It's highly likely that you had one or more bad-but-not-dead cables (like a weak termination) that was limiting your speed. By swapping everything out you fixed the problem. Cat 5e to 8 definitely shouldn't have caused that much if a jump (if any).

Cat5e works fine for gigabit. If it's not connecting at 1G, then the cable has been damaged and is probably connecting at 100M.

You should be seeing about 118MB/s in an iperf test on gigabit ethernet.

My guess you had broken cables or defective connectors. Because even on cat5 (not cat5e) you should get much more than 7mbit, or did you have coaxial? LoL.

In my experience 90% are plugs, specially if you crimped yourself with Chinese tools

CAT8 40MB/s

I think you went a but overkill with that one, high quality CAT6 cables would have done the same job, but hey, if it works, it works.

Your connection is 40MB/s I assume

5e is capable of getting the full 1Gbps of my connection so I easily see over 90MB/s. That being said I bought a big 100m bulk years ago and have been clipping it myself with care.

If you were indeed using leftover/ free cables of cuestionable quality it indeed could be a reason for poor perfomance

Cat8 is not the benefit here. It's all twisted pairs as any other CAT cable. You probably just had a shitty quality cable.

Cat 5e does 2.5Gb. Getting higher spec cables might increase the probability of them being well made to spec but other than that, what you really need is good quality cables, Cat 5e or otherwise.

You can get gigabit over 5e, you don’t need super expensive cables. That said I ran cat 6 through my whole house and am able to fully saturate the bus, about 115 MBps (920 Mbps) which accounts for the TCP overhead. I haven’t tried 2/5/10G on it bull I’ll probably upgrade in a few years, I don't expect to have much trouble getting good speeds. Your biggest issue was you might not have had all the cable pairs in your wire, or your cables ends might have been crusty, or you could have had bad kinks in the wire causing packet loss, or some real absolute trash quality wire. In general, 5e and 6 are plenty for most people/situations to get good speeds (1Gb+)

I'd be interested to see if you swapped the cables back if your local interface negotiated to FE instead of GE. I wouldn't be surprised to find that you've got a pair that's not properly terminated or broken and dropping you down to 100Mbps.

You've been using cheap cables.

Next step up is a JCAT: https://audiobacon.net/2019/11/02/the-jcat-signature-lan-a-1000-ethernet-cable/amp/

/s if not obvious.

40MB/s is no where near the limit of cat 5e. It can easily do gigabit.

I have stable ~950 MBit/s to the NAS with Cat5e. That's ~115 MB/s. If that 40 is to a machine on the LAN, either there is some bottle neck at one of the ends, or there's some problem with the cable to the RJ-45 jacks.

Also learned this the hard way, when i was starting my "homelab" , I bought a box of (not knowingly that its bad) cheap CCA(copper clad alum) cat6 cables and im wondering why are my access points not negotiating to gigabit, turns out cca are trash and shouldn't be used on POE or even on high speed trunks, learned my lesson now and swapped my cables to pure copper, they are more expensive like 100$ more expensive but at least they do the job.

Ethernet speeds historically were measured in 10/100. In my past life I worked for an a small rural isp. And part of my learning I was taught that cat5 was 8 strands of wire, or 4 twisted pairs. I got very familiar with crimping patch cables. If one strand were cut a network card would negotiate down to its lowest speed and still work at 10mbps. Operating on 4 wire or two pairs. It’s possible with those numbers you had a bad connection, or a broken strand in the cable and it auto negotiated down to 10mbps. To this day I still crimp my own cables, and I own a cheap cable tester to make sure the crimps and cables are good.