I don't think prices will come down shortly yet, as the futures on gasoline prices for singapore is still quite firm. (US (Kansas) has dropped about 8% over the past 4 days.)
Actually I did use Shell premium petrol in the Boxster in the past, but no noticeable differences in performance nor mileage, may be it is an NA engine and not that highly tuned, and I drive like an old lady!
Oh dear! That's bad news. I used to use ordinary Shell & Sinopec and notice no differences between power & mileage, nowadays 100% Sinopec (ordinary petrol).
Oh yes, I am a cheap ass, so ordinary petrol, no premium petrol for me!
But on the other side, i tried a few tanks sinopec with my IS with their premium gas and the performance and mileage dropped significantly, with noticeable vibrations when idle. After switching back to Caltex, the problem resolved.