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+)