While it may be true that we have a finite learning cap per day, different people have a different cap. I know folks who voraciously read everything and learn many new (and different) things per day, and I know people who can't handle that pace. It's dangerous to slap an average number on this and say that everyone is limited to that.
Appreciated the rest of your post, it highlights the importance of good documentation in optimally using systems.
I agree the 60 pages number is arbitrary, but I think if like the reader you are feeling overwhelmed it is a sign you are trying too much.
I certainly read much larger amounts of new stuff every day when I was younger, but I was also anxious as hell to the point where I blew many good opportunities and even had blood pressure higher than it is today despite the fact that the objective level of pressure in my life is higher than it has ever been.
Appreciated the rest of your post, it highlights the importance of good documentation in optimally using systems.