That didn’t seem right.  It seemed like the browser would have something to do with efficiency but surely the primary bottlenecks (for something so dramatic) would be network related, but I was running the uploads off of the local network and wasn’t seeing the same type of issues in any other browser/OS.

With a bit more digging, the culprit was found.

This issue occurs because the default Winsock Send buffer is 8 kilobytes (KB), and therefore Internet Explorer supplies the data in 8 KB chunks. On an average network, this equals approximately 80 KB per second (KBps), regardless of network bandwidth.

So, you might not bump into this if you’re running on a not-so-fast connection, but if your users are typically going to be on something nice and quick – there’s a fix here (via some registry changes).  Of course, the real fix is: update IE to the most recent version or just use Firefox.