What's reasonable will of course differ from one person to the next. Even if I had a full TB of data to back up regularly (I'm glad I don't) it's for me perfectly alright to let this simmer in the background while I do something else, because I don't need to actively oversee the transfer and I don't need it to be done in a hurry.

In another post of yours in this thread you mention that you have gone "all in on M-Disc" for your archiving, which come with much lower transfer rates (they typically max out at ~16 MB/sec last time I checked) and the requirement of actively managing disc swapping along the way. I'm sure you can appreciate the far more efficient option of a slow 2.5" SMR drive.

I appreciate this might seem contrary, but I see it like this: if I am using hard drives, I am using them for speed. If hard drive is only double the speed of Bluray, then its not a sufficient differentiator for me.

Enterprise grade, CMR 7200+RPM hard droves, on the other hand, are closer to ten times faster than uray, so more worth it.