The UAM and this plugin both look very promising and it appears the code is being revised for improving the efficiency. Check out this forum post as of August 2013:
Monitor the status:
Marcus Fridholm: http://wordpress.org/support/profile/marcusfridholm
A related forum post by Marcus:
"GM_Alex (the UAM author) have promised to look into it.
Basically the plugin makes a new set of queries for each item in each context, which will quickly run into the hundreds. Or in my case into the thousands, but that may be a fluke.
This means that mileage may vary: If you have many groups and many different locked pages, categories and media, it will affect speed.
If GM_Alex succeeds in remaking the plugin using fewer and more global calls, replacing the repeated db-queries with array-calls, the rest of the code is pretty efficient. "
Keep up your great work GM_Alex and thanks Marcus for your work too.