By user settings ?

Admin setting is what I would need. I would not expect users to be able to change this.

application/config/config.php
add this
just before 'components' => array(

    'params'=> array(
        'defaultPageSize'=>20,
    ),

See what you can update in config.php in internal.php

@GuernseyResearch: Is above solution acceptable for you?

Need manual update is solution is accepted.

That does work for me, although I set the number to 100. However, it does change the number of rows for all pages, which could be a problem elsewhere.
1 - it does need to be in the documentation with a bit more explanation.
2 - will it ever be impacted by a simple comfortupdate?
3 - could this be an easier configuration option (for perhaps just certain pages) in version 4?

Thank you for the assistance. I appreciate the help. It has made my process easier.

2 - will it ever be impacted by a simple comfortupdate?

No, except if we add defaultPageSize for different page, but i don't think it happen in a minor update version ( X.Y.Z : X is major, Y is minor).

3 - could this be an easier configuration option (for perhaps just certain pages) in version 4?

Have different defaultPageSize can be a New feature candidate. Maybe can be done in plugins ?