Mr. Blonde,
I'm changing every 3,000 miles because that is what is required to keep my warranty intact.
If you aren't worried about the warranty, then change the oil filter every 3,000 miles, and get your oil analyzed. When the analysis comes back as "time to change the oil" then do it. You can find out more about oil analysis at
www.bobistheoilguy.com which is an excellent site that covers more about oil than I knew existed.