Interesting mix of cars in consideration @archsteve
I have a caddy 4v-Blackwing edition... you described that car very closely, without realizing it. I use mine primarily as a long range highway missile, that can also tackle track days and weekends at the strip with zero drama. It is...
Big porsche guy here, so I may be a tad biased. Overall, the GT4 is a big step up, and even more engaging with a manual. IIRC, the brakes and suspension on the 981 GT4 were developed from the 991 GT3. Personally, I would pull trigger and not look back. Both are great cars and you will enjoy...