Images on a different subdomain. Better performance or not?

I keep reading that by putting images on a different subdomain on the same server as your main site can speed up page load by allowing more connections to be made to the server.

I thought I would give it a try, so I went to Media Settings, and for the field “Full URL path to files” I filled it out like this: http://img.example.com/wp-content/uploads

My server’s host record has a wildcard for subdomains, so I could use any subdomain for the media URL.

I’m having trouble getting consistent test results in order to know if this is an improvement. I would be interested in hearing thoughts or experiences from other people on this.

[No bumping. If it’s that urgent, consider hiring someone.]