Database Schema Design Question

Our company is having a large debate over what I think is a simple concept.

Here's the background.
We have 4 different entities (Lender,Guarantor,School,Servicer). Each entity has basically the same fields (Name,Address, EDNum,etc). Each of these entities has contacts which we store in a Contact table.

Here's the question.
Should we put each entity in it's own table? My opinion is to have an Institution table with an InstitutionType field which will then identify what you're looking at.

The concerns are this.
There are other tables such as Loan that references all 4 of these entities. The concern is that queries that reference 1 table 4 times will be much slower than a query that references 4 different tables. I realize that there are a couple of other issues, (such as if we had them in 4 different tables we would have to have another field in the Contact table to identify what entity we're talking about), but my only battle now is this join/speed issue.

The 4 different entities will not change much, so updates/insert/deletes are not much of a concern. It's just the viewing and joining that I'm wondering about.

David
headworks@usa.net