IT'S been on sale in Australia less than two years but already BMW has seen fit to power up its top-shelf 6 Series coupe and convertible. Gone is the previous-generation 4.4-litre V8 of the 645Ci, replaced by an altogether more persuasive 4.8-litre version that delivers a substantial 270kW of power - without increasing fuel consumption. While the V10-powered M6 coupe remains at the pinnacle of the 5 Series-based coupe and convertible range, the 650i two-door models represent even more convincing proof of BMW's engineering might.