Real World Item Level Permission Performance?

I am considering implementing item level permission on a list we use. I've seen all the articles online cautioning not to do this with lists of more than 1000 items, but the articles seem to have little detailed information about the actual impact and what causes the performance issues. Additionally, they seem to refer to document libraries more than lists. I'd like some feedback about what might occur if we were to use item level security in our situation.

Our situation is this: list of current ~700 items in a sharepoint list. Expected to grow around 700 items per year. The list has about 75 fields on it. We have 8 active-directory groups that have access to the list, based upon company department. Each item in the list can apply to one or more departments. The groups represent around 100-150 different unique users.

We would like to use item level security to be set via workflow, to enable particular groups to access the item based upon their group membership. For example, if the list item is for the HR department, then the HR group has access. If the item is for IT, then the IT group has access (and HR wouldn't).

That's it. There would be no nesting of items with multiple permission levels, no use of user-level ACLs on the items, etc.

Thoughts about this configuration and expected performance issues?  Thanks for any feedback!