I assume you want to test the server at 1,000 users since the browser only supports 1. The server can't tell an AJAX call from any other; as Billy Joel says, It's all HTTP to me. Can't you simulate the AJAX calls with any HTTP load tool?
A good question is never answered. It is not a bolt to be tightened into place but a seed to be planted and to bear more seed toward the hope of greening the landscape of the idea. John Ciardi