the single cracks are the start of proper det and not just the normal pinking that you get under load in alot of NA cars.

Thsi is the stuff that melts pistons mate so be careful.

I would stop testing it on the road yourself as you are probably damaging the engine.

On another note my old engine used to make good power fo rthe spec and had a good mixture but detted its tits off due to an oil burning issue. It was contaminatin g the mixture under high loads.

Sounds similar to your probs mate...