I have a 4.2L turbo diesel Nissan Patrol. I change the engine oil every three years/100 000km. The last oil analysis after I changed out suggested I could keep it in. Looking at the figures, the pentane (soot) levels would have reached maximum in another 40-50 000km. I used the oil to top up one of my trucks. Because the oil doesn't sludge up like conventional oils, I have not changed my main filters (I have 2) but I do have a bypass filter that I changed 3 times. No build up could be detected. Oil analysis said there was nothing to detect. Wear levels at 100 000km were far less than what is produced with conventional oils at 5 000km (recommended service interval for a Patrol). My savings: 20 services = 40 filters and 20 x 11L =220L of engine oil and 220L of waste engine oil I did not need to dump. Vehicle is at 383 000km and still going strong. I am definitely keeping Poly-ol-ester in my engine. I also use it in my earthmoving machinery and truck.
Most of the sludging that occurs is from the oil molecule breaking down into smaller chains. Many reasons for this that I won't go into here. One of the inherent weaknesses of mineral oil is it is easily broken down. Ie you don't need much of any contamination to start a reaction with the oil molecule. 99% of the advancement in oil technology in the past 50 years has been in the additives that try to control this and stop it happening. That is where the poly-ol-ester has a very significant advantage. At the temperatures seen in conventional engines, it is nearly bulletproof. Its operational temperature ceiling is nearly double that of mineral oils. If it is not breaking apart, then it is going to be doing its job of lubricating, not generating sludge.