Does anyone have experience with item-level security on list items?

We're interested to know if doing this affects performance due to
SharePoint having to apply security-trimming down to the list item
level before it renders the page.

Here's what we are trying to do:

Teams List - 30 items
- Used as the source of Lookup values

Secretary List - 100 items
- Each secretary belongs to a team

Assignments List - 500 items
- Each secretary team supports 1 or more people

All secretaries should see all other secretaries.
Secretaries should only see the assignments for their team because
notes on the assignments are confidential to the group.

We were thinking of creating security groups for each team and
restricting each assignment list item to a specific team.

On the web page:
1) Filter web part sending team choice to Secretary and Assignment
web part. Users can switch the view from team to team.

2) Secretary web part shows all secretaries for selected team.

3) Assignments web part shows all assignments for selected team. But
the logged in user will only be able to see the assignments for her
group.