In March, the longtime BMW collaborator Alpina launched its latest creation, the 2015 BMW Alpina B6 xDrive Gran Coupe, which is based on the body of BMW’s 6 Series Gran Coupe. The B6 is the first four-door coupe in Alpina’s portfolio of performance vehicles. The potent 4.4-liter V-8 biturbo engine of the B6 produces 540 hp and 540 ft lbs of torque, and it is mated to a BMW ZF 8-speed automatic transmission, with Alpina’s Switch-Tronic technology, that makes smoother and faster gear changes. BMW’s xDr…