I would upgrade your main 5 cars to 1,3 each path. Don't merge your A and B class cars yet, later on there will be a lot of easy yellow cars for the red, and I don't do A/S since they are good enough.
That Mustang GT is a monster when fully upgraded. I used mine for most of the late game in single player.
The civic is a lotus elise who goes +170 , nearly same stats
Sorry mate I merged mine to upgrade my A class Camaro which with that merge was the better car.IIRC the stats at 3.3/3.3/2.3 (or possibly 3.3/2.3/3.3) were 88 Grip, 3.7 Sec 0-60 and 170MPH top speed.
Everybody get that mustang gt !! It's a price for the final satge with the mclaren ?? Did not pass it...r