I just tried the demo and literally no issues (1060 6gb, i7-6700, 16gb RAM, installed on HDD). There was some hitching during the video playback in menus though.
I join the club that thinks the Porsche does not handle very well. It just understeers so much... The R35 is just a dream to drive, on the other hand.
But my overall first impression is very poor. I loved the cinematic and elegant style that both Forza 5 and 6 had, and I LOVED the action movie-like music during the races. In exchange, we got some trashy instrumental and totally forgetable rock in the background... Reminds me of the TERRIBLE soundtrack that Forza 1 had back in the day (Sorry, Junkie XL. You are awesome but it just dindn't fil).
Graphics-wise, the race at Nürburgring is a sight to behold, but the others not so much. I find disappointing how little has this game improved on car damage too.
The last Forza I thoroughly played and loved was Forza 3, and since I don't have an Xbox One I was eagerly awaiting for this new entry on PC. Sadly enough, it way below my expectations and I will probably wait for a good sale or just get one of Horizon 3 expansion packs.