I think it's a good idea.
Look at Audi, making it an A5, rather than a A4 coupe, makes it stand out more imo.
So a 4 series, despite it's unlucky sharm in the Asia, is an good idea imo.
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3 series: E30: 89 325i, E36: 92 325iC, 94 320iC, 96 320i Convertible, 94 320iaC, E46: 99 320ia, E90: 06 318i Le mans, E91: 07 318dt
5 series: E39: 97 520ia, 01 530Dat, E61: 09 520Dat
X series: E83 05 X3 2.0d, E84 10' X1 2.0 X-drive DA, F25 13' 2.0da X-drive.