I had some experience to share when I did a comparison in the past.
Situation:
Same track - Old TRC track
Same chassis and electronics - XRay T2'008 + 10.5R brushless motor
Same tyre - Sorex
Basically everything was the same, just the shell was different.
Shells:
- Tamiya BMW 320i WTCC
- Protoform Speed 6
By using Tamiya BMW shell, I can only consider my car was totally undriveable when comparing with Speed 6, at some corners, I can flat out when using Speed 6 shell, but with the Tamiya BMW shell, the car has to be slowed down quite a lot when going into the same corner. Overall, the lap time was at least 1 second slower when using that BMW shell..... I remember that the lap time should be around 13s per lap, so now having 1s difference, the margin is quite a lot indeed.
Can't share settings for those 2 shells with you because I had no interest on setting up my car for the BMW shell, I just had one run and then going back to the Protoform shell immediately.