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I concur. I think those intervals are pretty close. We have been changing the oil in my service fleet every 4-5k miles for 10 years now. We monitor the internals for sludge and so far so good. Our Toyota and Chevy trucks typically go 250k miles without burning oil or showing signs of sludge.

A simple way to spot oil contamination and breakdown is to check the dipstick regularly. As soon as the oil begins to darken in color it is contaminated and due for a change. This typically starts to happen in my Boxster at 6-7k miles so out the drain plug it goes. This change interval is consistent with Jake Raby's findings also.