Speeding up load times of the User Admin pages

I'm running a large multisite with approx 10,000 users - more will be added each year.

The network admin user page takes ages to load (/wp-admin/network/users.php). Is there anything I can do (plugins perhaps?) to speed up page load? I don't know if the multi DB would help with this as the users tables is only one table:

Also - on a related note I find it REALLY hard to search for users as the default user search doesn't filter by username (login) which is how I identify people. Any solution to this?

many thanks,

Alex Furr