SuperMAG said:

Why not just post the User Id number to the required place. like if you want him to read or edit the page just post his id number.

Because most people like to select users by name and wouldn't want to type in a user id.

If many of those users are WP Subscribers, you can partially alleviate your loading problem by activating the following options on the Advanced Tab of Roles>Options: Limit eligible users for Post-specific editing roles, Limit eligible users for Page-specific editing roles

I know the ultimate solution here is to replace the user/group checkbox interface with Ajax. If total users exceeds some limit, the "eligible users" checklist would be downloaded and displayed dynamically based on search text. I expect to do that eventually. But since that feature will mainly benefit large sites that would presumably have some budget, I'm not prepared to donate that development in the near future without some support commitment.

scarlin said:

Might there be another temporary or partial solution that doesn't involve taking away the ability to give single users access to edit individual posts without giving them full editing rights?

My site has 4,000 members loaded in so this is an even bigger issue…on slower computers the browser is entirely crippled. We aren't a large site with a budget - we're a student government organization, and plugins like yours are what allow us to achieve the functionality we're looking for within our limited capacity. For that we are most grateful!

Any advice would be greatly appreciated!

What do you have in mind? What type of checkbox-limiting criteria would work well for your site?

Do you only need Administrators to assign the post-specific roles? What about an option to eliminate the role metaboxes from the Edit Post/Page Form completely, letting Administrators do the assignments (and deal with the slow page load) in the bulk admin forms (Roles > Posts or Roles > Pages)?