I just got my extender a couple months ago and tried this once already. Didn't notice too much of a difference in driving manners on 93 octane. Going to put in an old O2 sensor and some race gas in to try that out. Wanting to figure out a way to run the car without killing the O2 sensor. I have a used heated O2 sensor to try also at some point. I wish I could buy 100 unleaded around here!
I believe TurboBob said that if you run the Extender open loop, it still reads the O2 sensor even though it is failing. Maybe that would affect driveability some, but at the track under WOT in PE mode, power enrichment mode, it should work. Maybe following the O2 readings with the understanding that they will be fading and tune by kr.