I’d better measure that oak trunk. There’s also a big beech.
Do you have a couple of batteries for your chain saw?
I just have on battery. My mower battery will fit and has 3x as much power, but it might upset the balance of the saw - because it is also 3x as heavy. I think the mower battery weighs more than the chainsaw.
I think 20cm circles is viable. My idealized target is 25-32cm.