BMW 5 Series (2015) is 529 mm (20.83 inch) longer, 59 mm (2.32 inch) wider, 170 mm (6.69 inch) higher and has 398 liters (14.06 ft3) bigger cargo space than Porsche Cayman (2016).
Porsche Cayman (2016) is 435 kg (959 lbs) lighter than BMW 5 Series (2015).