It's a rare car in good mechanical shape that limits change intervals due to metal particles. If the chunks are big enough to cause damage yet not be picked up by the filter then wrong filter. If there are so many that they're a problem on the first pass then goodbye engine. Metal points to other problems which destroy the oil. Iron or aluminum, or even bearing material are all normal to some degree and point to their own problems of contamination or breakin/abnormal wear. More of a warning sign than a problem in itself.
What generally happens at oil end-of-life is the oil goes out of grade, either thinning or thickening, it becomes unable to deal with the chemistry influences of fuel and water or other contaminants, and it stops protecting your engine. Somwhere along the line it fails and becomes part of the problem. How quickly this happens depends on the specific engine and condition combined with your driving patterns and habits. Some cars are unique and need an exceptional oil to even hit 3K safely.
I agree that there's no guarantee besides fresh oil. Pushing changes out is either a risk done blind, or an extra cost to pay for analysis. I've seen dino's & blends go past 7K, and synth beyond 12K all backed by oil analyses. (my own results and far from extraordinary) So in some sense I think we agree. If your warranty doesn't require it, you aren't running harsh conditions where the improved cold cranking and flash points help, or extending the interval isn't useful, and you don't need a new hobby, dino at 3K is simplicity. I stick to it myself unless I know the engine can go longer.
Hey, isn't there an oil thread around here so we can leave Gilda alone?
