I filled up with a tank of 98 (or at least that's what I asked for). Within 5 minutes from driving out of the forecourt the ECU on my Forester dialed back the max boost to 5 PSI instead of the usual 20PSI - the ECU does this when it detects an engine knock.
I suspect I got a load of bad fuel - either the chap put in 95 (but even then I've not had this problem come up before when I've accidentally put even 92 in!) or more likely SPC Balestier has crap fuel.
Once I got to 3/4 tank I went and topped up with some Caltex 98 - sloshed the tank around hard - and the ECU dialed the boost back up. Prior to this I could actually hear the predetonation on boost as well as see the boost gauge dialing back at the same time as the ECU shut down boost so it was not just my imagination.
Might be best to avoid SPC Balestier Road for a few weeks until their bowser tanks are refreshed if you drive a car sensitive to RON.