I have been using caltex, shell and total engine oils from 1984 but then last year I tried ZIC and found X7 5W/20 and 10W/40 fantastic. Twice a year flush your car engine with diesel. Drian old oil. Now pour 1.5 to 2 liter diesel (or make a mixture of diesel and cheap oil 1 liter each = 2 liter engine flush) and start the engine and let it run idle for 10 minutes and do not race the engine. Now completely drain dirty diesel and replace oil filter with new one and add fresh ZIC oil. Excellent method to flush all contamination from engine with no harm at all. Regarding PSO engine oil quality I have never used them. However, packing of PSO oils is quite good. Once or twice thought to use it but so far not tried. But one thing I am pretty sure that nothing can comes close to ZIC. ZIC is # 1.