Put gears on the bike that fit you perfectly, i.e. the Pinarello, it make sense to make it even more comfortable, especially on the long ride from East to West just to have some pints.
I feel it would be idea to run the Simoncini single speed for now (with chain tensioner) so you can decide whether you want to put gears on it or not, it would be a waste if you spend age and money getting all the component for it and end up finding that you don't like how it ride.
Put gears on the bike that fit you perfectly, i.e. the Pinarello, it make sense to make it even more comfortable, especially on the long ride from East to West just to have some pints.
I feel it would be idea to run the Simoncini single speed for now (with chain tensioner) so you can decide whether you want to put gears on it or not, it would be a waste if you spend age and money getting all the component for it and end up finding that you don't like how it ride.