When running higher octane fuel, you are 'delaying' the onset of pinking. Pinking is bad for engines. When it is detected, the ECU winds the timing back by quite a bit (11 degrees?) and then advances it in 0.5 degree increments until a point just before pinking occurs again. This is what happens with the VR6 and I expect similarly with the 20VT although I don't know if the 20VT can detect which cylinder is pinking and independently control the timing like the VR6 does?
Pinking is more likely to happen in hot operating conditions - a hot day, or if you've been driving hard. I suspect that the effect of backing off the timing in a Turbocharged engine will be more marked than in a normally-aspirated one.
Pinking also has a effect of raising the engine temperature so it has a 'self-perpetuating' quality too. The trouble is that even if you can't hear it, pinking has to occur before the knock sensors can detect it so there will be some increase in engine temperature.
So in short, running higher octane fuel will result in lower engine operating temperatures, with all the benefits that brings, and SHOULD help reduce the occurence of the hesitation problem.
My car has only ever run on Optimax from new (5500 miles) and has octane booster when on track days.
