You know this is somehow related to a "bad" batch of gasoline, so check all the basic gas-related stuff.. Check and see if the carb is still clean and that fuel flow out of the tank is good.
... may have (during the panic) unintentionally changed something else that affects proper carburation.. perhaps throttle linkage or choke operation or something.
Maybe that new spark plug is a bit loose.. Double check everything/anything.
Although it ran on too little oil for a short stretch, moderate operation for less than a mile is nothing... unlikely to do serious damage. The engine already had an internal coating of oil and you did say the bad batch had some oil?
If the piston rings were damaged power would suffer a little... they would not seal as well and compression would be less, and pulling-torque would be less.
Since it runs normally on the flats, i'm kinda skeptical about the possibility of ring damage, although it's possible. Low results from a compression-test might reveal it if you already know what the normal, healthy compression on that engine should be.