I'm curious what kind of testing automakers do for OCI recommendations. The only testing I've seen in this industry is dyno testing, which pretty much means continuous running of the engine. Sure, they include wide open throttle and full load in the regimen, but I doubt their testing includes the amount of cold startups experienced by the everyday driver.
If I ran nothing but highway in my vehicle, I wouldn't hesitate to extend my OCI to 6000, or even 7500 miles, which I have done for long trips.