I've got some relevant experience so I'll chime in.
I went from a 2014 Cayman S 6 speed to a 2015 C7 7 speed. I had the car 3 days and wanted the cayman back. 3 weeks later I sold the C7 and ordered a 2016 Cayman S.
the c7 lacked a level of precision and integration that german cars have. It just feels kind of sloppy in comparison in so many ways. I suspect the C8 will suffer from that same feel. How much that matters to you is a question you have to answer.
the c7 is also annoyingly big and hard to see out of. Those things actually matter when you drive the car, especially in a city. The C8 is even bigger.
Longing for normal aspiration, strong low end torque and a manual transmission I recently considered the C7 again, since there are really no other options with those three characteristics out there. I went to see one and even just sitting in it, it brought back all the bad memories
I've since ordered an M2C.
I will say this, make sure you go for a LONG test drive with the C8 and M2C before you make the decision. I went for a short 10 minute test drive with the C7 and it wasn't enough time to properly assess the car and feel the fit for me, and so I ended up with a car I didn't want to live with.