I recently upgraded to the new official Sprint Touch WM 6.1 ROM, so I decided to test this out last night. I did multiple tests on speedtest.net, using multiple servers. The download speed remained about the same, but my upload and ping speed was consistently twice as fast with the setting set to "enable".
Here's the first set of tests, with it set to "enable":
Here's the second set of tests, with it set to "disable":
And here's the final set of tests, with it back to "enable", where I left it:
