Worst case senario, preignition that buries a connection rod into the crank and tears your engine apart. Or, maybe nothing. If I were you I wouldn't run less than 89 in that engine. preferably 90 or 91.
??????? if your running octane lower then what's rated for your car you run the risk of detonation. Bad stuff. The higher the octane the higher the flash point. More compression=more heat, needs higher octane. As for your your question directly, I don't think so but then again I don't know. I would imagine using lower then required quality fuel is bad regardless of what ammount of throttle your using. Is there something amiss with your car??
No if your engine was experiencing preignition it would ping more as your revs increased. It sounds like you have a problem with either air fuel or spark. Can you give a more detailed description of what the engine is doing and when it started?
i would check your plugs, make sure they are gapped properly and don't look odd (rtfm). take a look at the distributor, too. and run a few gallons of mid-grade fuel (from a good gas station), along with some water-removal stuff. you may just have a little water in the fuel. or diesel.