Overview 

The problem might be associated with the default SendBufferSize value in the Apache httpd.conf file.  Windows seems to completely ignore this value and Apache will use the default Winsock value for the buffer size (4096). 

This value can significantly reduce performance on High Latency/High Speed links when set too low.  You can change the default value in Windows so that Apache will then use this new value.

Instructions

To change the default value in Windows:

1. Open regedit and browse to:
   HKEY_LOCAL_MACHINE > SYSTEM > CurrentControlSet > Services > AFD > Parameters
2. Create the following two DWORD values:
   DefaultReceiveWindow
   DefaultSendWindow
3. Set both of these values using DECIMAL (not Hex) through the following formula:
   DefaultReceiveWindow = (Download Capacity in Kilobits * 1024) / 8 
    DefaultSendWindow = (Upload Capacity in Kilobits * 1024) / 8
   
   For example, for a 10Mbit (10000 kbit) upload and download:
   DefaultReceiveWindow = (10000 * 1024) / 8 = 1280000 
    DefaultSendWindow = (10000 * 1024) / 8 = 1280000

Note: Adding the above registry values may help you gain a substantial (up to 10x) performance boost.