I have a proprietary app, written in Java, that uploads files to a server via multiple HTTPS POST requests. There's a Mac version and a Windows version.
On the Mac, we easily get 3-5mbps upload speeds. Nice!
On Windows machines we've tried with a comparable processor speed & RAM, the upload will very often cap out at 800kbps. (Though on my Windows 7 machine, it won't do this.)
A lot of people are still using Windows XP. Could that be an issue? Is there anything else we should keep in mind?