I always thought of Porsche as drivable supercars and that's why I've always been a fan. You try and daily a Ferrari or Lamborghini of that era and it won't go a week without needing major maintenance.
But even then,
the yellow bird was a development of a Pcar by a tuner, so does that really count? Performance wise, sure.
Of that era, the 959 was definitely a supercar, maybe the first supercar. Top of all the Porsches, and still a very desirable and valuable investment. The performance would seem tame by todays hot hatch standards, kinda, and really tame compared to the new Vette's.
I still see the 959 as a Supercar. I don't see the modern Vette as one.
So definitely not considering performance alone, I think it needs to be taken in context of the times too.
And of course most of this is subjective and even personal opinion. But even if I hop up my Suby STi / Mustang / Camaro / Vette to insane levels of power and handling, and I smoke a GTR around the track, that does not make my POS a supercar. Sorry Rugger, your V8 Miata would beat most stock Supercars around a track, but they leave in their supercar, and you leave in your (not so gay) Miata
Of the same era more or less as the Ruf cars, I would consider the Lambo Countach S as one of the supercars. Probably as many posters of that car as there were of Farrah Fawcett. By todays standards the Countach would be outrun by a Mini CooperS, and you sure could not live with that car as a daily driver without major sacrifice. Again, Countach remains a Supercar in my opinion, the Mini, probably not. (although a really rare specimen, a record holder at PP
)