My preference is to use the tail that was first used on the '75 Carrera, then again on the '80 Weissach edition cars. Spoilers make a big difference in how these cars drive. For what it's worth, I don't like any tail on a targa or cab. I also don't like the 3.3 turbo tails on a narrow body car, or the all rubber tails on any car. I like the '75 Carrera tail better than the '75-'77 turbo tails or the 3.2 Carrera tails.
Here's one on a Carrera 3.0:
Image from flickriver. All rights reserved by Tim.Walker