To be honest, how much longer will the NA engine be in the GT3s .... it is possible that this 991.2 GT3 and RS will be the last batch of NA and every future 911 (including GT cars) will be in turbo form .... like the upcoming GT2 RS. So it won't make much difference as all 911s will be turbocharged. By then, a GT3 may not have that much of a difference than a 911 Turbo.