I think
@virtualmacho has it right. DV cars fly under the radar, while cars like Magma and Hethel attract radar. Overall DV cars are faster than Magma and Hethel cars, because those cars spend more time on the side of the road after being pulled over by the police.
Nimbus cars aren't as fast as DV, not because they can't be, but because they're trying to blend in. Driving fast would make them stand out.
Shadow Gray cars are almost as fast as DV cars, except they tend to slow down when going through shadows... some kind of self-identity thing.
Now Seneca cars
are special, but being blue, they tend to be moody; so on an overcast day they slow down. In the bright sunshine they do well, although they like to socialize, so stop a lot to chat with others. They like lots of praise and the comfort of affirmation hugs.
As for DV cars being more comfortable... not sure on that one. DV cars are for the drivers, so their focus is on the road. DV owners do appreciate proper etiquette however, and will cheerfully wave at every other color Emira as they pass them by.