Fastest and simplest access control for specific nodes

Hi,

I want to create a basic calendar using the CCK/Date/Calendar modules and the users should have a way to choose between public and private Events.

There is no other access control beyond plain Drupal permissions on the site. The site is on shared hosting and already a bit slow so I'm looking for a module that has the least perfomance impact on other requests for that site, that don't need any access control.