[csbear]

That's a tough one.

My brother has a manual 2016 991.1 GTS which I have driven a bunch. I felt my 981 GT4 was the better driver's car though and just more exciting.

At the end of the day, the 991.1 GTS is not a GT Porsche. It is a value package Carrera S with what?...additional 30 hp.

Don't underestimate what the M2CS will be in comparison just because one is a BMW and the other a Porsche. In it's totality, a brand new M2CS will have many pros over a 2016 991.1 GTS:
1) CS will 'feel' faster on the streets... 430 NA (which is awesome btw) vs 444 twin turbo (which is awesome as well for different reasons)
2) CS will have better amenities and more modern interior. The 2016 GTS interior is not that good in comparison...
3) CS will have the rarity and honestly the cool factor as well (if that's important to you)
4) CS with a little more practicality
5) New BMW with maintenance covered for sometime vs potentially expensive 991.1 GTS repairs on the horizon
6) You already love your M2C

Obviously, a major difference between the two is the weight difference and chassis... the great equalizer in favor of the GTS.

I say go M2CS, unless you are ready for something different in the 991.1 GTS, which is a great drivers car in its own right.

Edit: I just see the 24hrs have passed. Either way M2COMP goes.. it's a win-win.