Thanks for the reply.
I'm in Arizona, so we're stuck with crappy 91 octane. The dealer already tried to blame it on me getting the wrong gas, but I've only used 91 since I bought the car. The car has been knocking/pinging almost constantly since this past summer - and it gets much worse, as you might imagine, if the outside air temp is over 65 Fahrenheit or so. Usually pretty audible pinging under moderate to heavy throttle starting at 4k RPM and going up from there. Car is usually very sluggish, as well, despite ECU resets, etc.