Doesn't the GT500 and it's 660hp engine avoid the tax? Surely BMW, with a smaller turbo charged engine in a much lighter vehicle, can avoid it in the M3/4.
I have nothing to base this off of, but I'd expect it to not get too terribly worse economy than the 335. I'd guess somewhere around 23mpg combined and nearing 30mpg on the highway. But maybe I'm being optimistic.
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