I'm fairly sure that the RON specification by car manufacturers for the fuel to use is a minimum requirement, enough so that your engine doesn't knock. So it shouldn't hurt to use 98RON. But feel free to tell me if I'm wrong
The map adjusts automatically. There's a minimal difference, but it's most noticeable in pickup when it's hot and aircon is on. Other than that, minimal difference but mine does run quieter on V-Power...
My A2 is a diesel but being surprised Audi would supply a petrol engine that runs 91 ron I decided to look at the engine spec. Compression ratio 10.5 to 1.
I have two petrol engines with that ratio and both get the highest ron petrol I can buy. They run smoother, accelerate faster and give better economy that more than compensated for the increased fuel costs.
Standard unleaded makes the engines feel constipated and prone to stalling. Give some 98 a try; I suspect you will be pleasantly surprised.