Well, I wouldn't dare to guess when it comes to the RT12
I remember reading an article about Ruf, they handed the spec list of the CGT over to the big cheese of Ruf automobile. After looking at the figures he replied with "well that's a slow car"

8) And then the RT12 came along.
So, 5.7 V10 If you have seen the vid of the GT street before then you have probably seen the vid where it hits the barrier as well ?! Also availible on youtube.
Cheers