Dear JP: The minimum octane fuel for the RIII as recommended by the owner´s manual is 91 octane using the average of the research and motor methods of determinig octane. In the US, this is a medium grade fuel, not the cheapest nor the most expensive. In Canada, where I have also ridden extensively, two grades of fuel are usually available- 87 octane and 92 octane. The RIII would, of course, require the 92 octane.
As far as city driving as opposed to motorway driving is concerned, I too live in a fairly congested city although I suspect not as congested as Madrid. The wonderful thing about this bike in my experience is that it is as smooth in the city as on the motorways. The company has been able to program the fuel injection system such that it is smooth at almost all speeds. The turning radius however is quite large and you may experience difficulties in turning it around on narrow streets. Of course, in congested city driving fuel consumption will not be as favorable as on the motorways. I hope this helps you. I do not think you will be disappointed in the performance of the bike in city or motorway driving. 
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