I have a BMW 540i that has 320,000km on it running inboard service intervals (around 20 - 25,000km between changes) and runs like new. It gets the only certified oil for the 4.4l V8 which is Mobil 1 0W40.
I have personally put over 200,000km on a Datsun (Nissan) 260z in 5 years running 15W50 synth at 10,000k intervals (also Mobil 1, but I'm not necessarily brand loyal. We just get an excellent price at our local depot.)
The particle size that gets through your filter shouldn't make a difference if your oil is doing its job, that is; keeping the metal parts seperated. Think of how long Diesel engines last and they send the oil pitch black in several hundred k's.
The main things (and I'm no tribologist, but I do know a thing or two about mechanical design) with oil are its retention of viscosity and it's total acid and base numbers.
If the TAN and TBN stay acceptable, and your VI stays fairly stable, then your oil is still good.
My main client uses this rule (checked through SOS) on machines that are worth millions of dollars (think 34 litre twin turbo V12's
). If it works for them it works for me. Each to their own though.