Normally with a BM I would suggest a bigger engine but the 520d has excellent performance figures allied to wonderful fuel economy for a car of its type. According to Parkers, the previous 5 series was often referred to as the best car in the world, the new version is longer, wider and faster. So, if the 'slightly unusual' styling sits well with you it would appear to be an excellent choice. The resale value should also be bulletproof !
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