We use MediaBeacon for digital asset management and our end users upload files from both Windows machines and Macs to the MediaBeacon servers at a datacenter. The Windows clients can upload a 1.5 GB file in 30 seconds while the Macs on the same network take about 3 minutes. I was also able to upload the file in 30 seconds from a Windows VM running on my Mac (VMWare Fusion using Bridged Networking to the NIC on my Mac). We use a web interface to upload via HTTP.
So it appears to be something within OSX, is anyone familiar with this constraint and how to get around it? thanks!