Has Indy 10 Supercore not over 4000 connections too?

I am writing a TCP Server that has persistent conenctions using Fiber of Indy 10's supercore.

For test, server only accept to connect from client.

With Indy 9, I found that the number of connections is not over 2000.

If thread stack size reduce, connections increase to 4000

on my test server(1GB RAM, Windows XP).

Why can the number of connections over 4000?
(on stack size is 1 KB)

I  hope that the fiber of indy 10 solve it.

However, the result is the same of indy 9.

I want to know the method that solve its.

Thanks
James Yoo