Using 93 octane for a tuned 1.8T for 91 octane if anything will run a little better, of course it probably won't increase the power output of the engine at all.

 

Well.. preignition is not the same as detonation.
'Knocking' is detonation and is what your ECU compensates for. Preignition snaps rods and there's nothing your ECU can do.

Best thing is to test lower octane on a hot day under load (up hill at 3/4 throttle, dragging brakes, etc). If you hear it ping, use a higher octane all the time. If not, your ECU can adjust sufficiently and you prolly can go lower. If there's even a hint, stick with premium. For every ping you can hear, there's more cant.

 

I was actually thinking higher than 93. I know its not practical for everyday use but what about 100. Just curious.

 

In order to take advantage of higher octane, you would need to re-tune the ECU. It can, and is, done. One program for everyday, another for race day.