AFR and scale does matter if using say a Racepak set up. It is WAY easier to kill an engine going FAT than it is going lean. Especailly if one id 10-1 on a stoich scale of 14-7. Way easy to stick a ring from heat of being fat than lean, microwelding of ring lands happens from being overly fat and not that uncommon especially with certain fuels. That heat can be enough to burn a piston top but have to be pretty extreme for sure, but this application woudl be extreme. Two O2's for race tuning are almost useless in all out effort cases. Its an average only if one cylinderis WAY fat it will just drop the average number. If he was 10-1 AVERAGE that hole could have very well been well in excess of that. All race fuels have an ideal stoich number, some prefer lambda but that number is not as easily found from most race fuel manufactures. You could convert that but as I say most use Stoich racepak can use either if changed to lambda