In a past life I oversaw Fleet Management for a police department. We maintained 100-120 vehicles. Oil was always low bid and bulk. Most vehicles saw 5k intervals. Many of the vehicles ran 24/7 with little down time and thousands of hours of idle time. Vehicles operated in city stop and go driving. Now this is strictly an observation on my behalf and not based on science. We never had any of the used oil analyzed.
We would replace 2-3 engines a year. No engine was replaced due to oil failure. If my memory serves me right, the Ford 4.6 lt engines replaced were because of hydro lock. (Operator Error) Ford Explorer 3.7 engines replaced were due to faulty internal water pumps that contaminated the oil and thus had major failure.(engineering Issues) The Chevy Caprice 6.0 were just pure junk and had engines replaced under warranty. Chevy admitted there were cam shaft issues. (Manufacturing/engineering issues) A Chevy Tahoe 5.3 overheated and had to be replaced.
We used bulk Gulf, Wolf's Head, Shell, Oilzum and Pennwood Oils. Mileage varied from 10k-65k a year per vehicle. I have seen many of these engines with valve covers removed or in various stages of repair. I never saw engine sludge. I only saw clean internal parts with minimum discoloration and varnish.
Based on my experience, I believe any oil API certified would be sufficient for the average passenger vehicle under all conditions. I think a lot of the acrimonious banter on these forums, well is wasted time, although it is entertaining and some of the forums quite informative. As for me, I use quality filters and brand name lubricants that are on sale. I've been maintaining my own vehicles for 40 years and have never had an oil issue. Save your money!