Just want to raise the point that once the 992 is out, there is a chance that all 911s will go for turbo. If the GT cars are also using turbo engine, the only thing that can differentiate the 911s is perhaps the type of turbo used (and maybe, as you mentioned, their respective weight - as the GT cars should be using more light weight materials). As such, there is a chance that driving characteristics of future 911 models may be more similar to each other than now (as the GT3 and GT3RS are still NA).