BMW 4 Series (2020) is 390 mm (15.35 inch) longer, 52 mm (2.05 inch) wider, 90 mm (3.54 inch) higher and has 278 liters (9.82 ft3) bigger cargo space than Porsche Cayman (2015).
Porsche Cayman (2015) is 195 kg (430 lbs) lighter than BMW 4 Series (2020).