EDIT: I would love to be proven wrong!
I know these aren't spectacular times, but these are times I've run on the snake tracks with the muscle cars over the few weeks I've been on Live.They should be easily beatable with a bit of tuning especially for twisty tracks and a bit more practice (most of these are from 1 to 4 lap runs) but I think they do show that the D Class muscle cars can be competitive even where you can't make use of the "missile" attributes.
TT Copperhead (D400 '69 Charger) - 326th out of 600,000+
TT Boomslang (D400 '69 Charger) - 4,440th out of 500,000+
TT King Cobra Reverse (D353 Chevelle) - 673rd out of 3255
TT Russell's Viper Reverse (D400 '69 Charger) - 2,999th out of 500,000+
'm not trying to show off, just prove Hop wrong!

As you can see, some are decent times, some aren't, but my point is that even on the snakes it is possible to get a respectable time in a D Class muscle. So, I think this idea has legs, but first I have a 71% career to get through and a Del Sol to build....