Shell 93 only. If BT ever comes out with a scan tool for our cars you can datalog and you will see the engine pull timing if you use lower octane gas. I did this with my previous car and switched from Mobil to Shell and never looked back. You might not notice this during normal city driving where you max out at <25% throttle under light load, but do a 3rd gear WOT pull to redline and I guarantee you will see indications of the ECU reacting to knock if you put less than 91 octane in the tank.
Jimefam - I wonder if that MS109 you got was bad. It doesn't make sense for the traps to go down - even if the car didn't adjust for the higher octane I would think they would stay nearly the same, all other things equal.