Pinging is a mystery to me. Ive read that the older an engine gets, the more octane it needs. My engine was designed to run on 87 octane. But in the summer, I have to use 91, otherwise it will PING like no ones business. In the winter, I can use 87.
I will probably throw in a good PEA cleaner a few times per year and see how it goes. The V70 runs like the engine is made of silk and I would like to keep it that way. It runs about 5C hotter than the Prius and doesn't have the same heat/cool cycling while driving, but the engine mostly loafs along between 1400 and 1900 RPM which could lead to the same trouble if I don't stay ahead of it. I have been watching timing advance on the SGII to get a baseline for where it should be.
The last car I owned that pinged was my 1987 Nova , with its carbureted , gutless , 1.6 liter engine. I sometimes ran 89 octane fuel to prevent it, but mostly just used less throttle at lower rpm. Never noticed in any of my fuel-injected cars.