Here is a tier list of all the cars (no trucks, SUV's or vans) in the game based on the quarter mile times of their best performing street-legal production variants (manual transmission unless none was offered). S: eSBR (9.429) A: K-series (12.497), SBR4 (11.670) B: Bluebuck (13.084), Sunburst (12.870), Bolide (12.723), 800-series (12.523) C: LeGran (14.243), I-series (14.230), Pessima 80 (14.044) Barstow (13.591) D: 200BX (15.270), Miramar (15.138), Pessima 90 (15.097), 150 Corse (15.070), Grand Marshal (14.857) E: Covet (15.644), Moonhawk* (15.551), Pigeon (15.444) F: Burnside (17.164) *The Moonhawk Special would have performed better than the tested Moonhawk Sport 4MT, but it lacks license plates and is therefore not street legal.
I always assumed the reason for the Special not having license plates was not having anywhere to put them. On the Moonhawk, the plates go on the bumpers at both ends; the Special started with no bumpers at all before switching to unique filler panels at both ends. The devs likely don't want to/never bothered to add the option to add a license plate to both sets of parts - especially as it is sometimes possible (even if it wouldn't be in real life) to have them both installed at once. Piccolina is sort of the same way; if you remove the rear bumper you can only have a Euro license plate.