REST-like queries run very slow if fetching only 3 records at a time

On internal intranet the C/C++ client sends out REST-like queries via TCP/IP and receives an XML response from the Java server. If the REST query loops fetching 3 records at a time, the total time to accumulate 90000 records is about 10x longer than if we fetch 100 records at a time. We will be performing a number of timing tests to isolate the cause. In anticipation that the problem may be the slow TCP/IP start due to initial small windowing, what settings are there to tell TCP/IP to start off with the largest (or larger) window size possible?

We are on 64-bit RHEL servers, and I assume that since the client/server are run on an intranet self-contained within the company, that we do not have to be concerned about congestion.

Thanks,
Paul