I had a 992 C2S before the M8. While it was probably the best "driving" car I ever owned - it was NOT a 6 figure car. More a Miata for rich people ..
. Materials were "ok" at the most, fit and finish sub-par and the infotainment an absolute joke. Dealership experience also nothing to write home about .. you want a loaner? Did you make a reservation 6 months (!!) in advance? When I complained about the performance of the infotainment (took like 3-4 minutes to boot) - I was told: "yeah .. we know ... look at the Panamera ... even worse". That was it, no fix. Performance wise the C2S is quite different than the M8 (mine was actually tuned by M-Engineering to ~600hp). Not much down low - you've got to rev and then oh boy ... all hell breaks loose. But let's be honest ... most we do is putzing around in traffic .. a little bit of back road driving here and there - but no track work at all. And putzing in traffic at low revs .. the TT V8 in the M8 feels like 3x as strong as the 3 liter boxer. I also like the amenities the M8 has to offer. Better materials, better craftsmanship, great infotainment, great engine sound. The 911 only beats it if you want to impress your neighbors.
And btw ... the engines of the S and GTS are exactly the same (just different tune) - the base has smaller turbos.