Unveiled at EICMA in Milan last week, the Aprilia RS 660 is one of the most aesthetically and technologically advanced concepts to break cover at the show. While there’s no current word on the RS 660 concept going into the production, the bike is set to boast a 660cc parallel twin-cylinder engine derived from the V4 powerhouses used in the Tuono V4 and RSV4 1100 Factory.