API Test Harness

I am setting up the Test Harness and had a question about the Max connections and Thread.

Would API/web service connections from two external servers supporting a total of 1000+ total simultaneous users be looked on as 2 connections and ~=500+ threads for each of those connections or would it look more like ~=1000 connections with a couple of threads per connection?

What would you set your settings at?

Thanks,