It is quite widely accepted that high performance turbo cars e.g Octy VRS benefit from/require super unleaded and in fact are less powerful on the standard 95 fuel. It is also a debated topic that your conventionally aspirated cars sometimes benefit from improved economy to the point that it just about pays for the difference in fuel cost (my experience with my old 2.0 Octy). The question is although the recommended fuel for the TSI is 95 (minimum, although it can run on lower with reduced performance) will it have the knock sensing capability (as a turbo) and the mapping (to optimise ignition advance) to get the benefit of higher octane petrol?

It will have a knock sensor (that's how ECU's can tell the difference between fuels) but since the engine is optimised for 95, using 98 takes it away from its best performance area. High performance engines are optimised for 98.

You'll only be able to really answer this question with some scientific testing. Dyno the car running on 95. Then run the tank right down and fill with 98. Run that tank down and refill with 98 again. Now dyno it again and compare. That will tell you if it produces any more power. Economy you will be measuring in between, as long as you ensure that you drive the same way with both fuels.

My feeling is that the 1.2 won't see any noticeable gain from 98 RON.