Here comes another one:
BMW M performance line's vs the "real" M GmbH's powerful 6cyl high performance engine technologies... I need a M4 - so badly 
Head to Head:
BMW M135i (Automatic): 2979 cc R6 turbo (N55B30)
Weight: 1515 kg / 3340 lb
Max output: 235 kW / 316 bhp
Weight to Power ratio: 10.76 lb/bhp
Max torque: 450 Nm
Sprint 0-62mph: 4.9 s
Top speed: 155 mph (limited)
BMW M4 Convertible 2979 cc R6 biturbo (S55B30T0)
Weight: 1825 kg / 4023 lb
Max output: 317 kW / 425 bhp
Weight to Power ratio: 9.62 lb/bhp
Max torque: 550 Nm
Sprint 0-62 mph: 4.1 s
Top speed: 155 mph (limited)