Oz... it surprises me that you'd put so much emphasis on performance for dollar. For the $40-45k a 328i costs, there are a number of 300+ hp cars that will out perform it. The 328, like the Vantage V8 though, is about style, comfort, status AND driving enjoyment.
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As others have said, I'd much prefer the Vantage coupe to the convertible. Same with Porsches too though...