Maxing out 1 Gb/s was no issue with HDDs 15 years ago. Maxing out 10 Gb/s is no issue with SSDs today. 1 GB/s is nothing for them. You would need 100 GB/s to have a buffer for the next 3(?) years, then it will be maxed out again.

In any case, a backup can take 1 or 10 hours, seems irrelevant in a non-commercial environment. Since people will be backing up to large HDDs in the foreseeable future, 1 Gb/s is just fine. 18 TB HDDs could potentially be 2x faster, say 200 MB/s. Not much to gain.

On a side note, I put cat7 everywhere back in the day. Maybe 150 meters.