Small addendum, the last quoted figures indeed seem to be correct.
Just received message from friend who's a technician in a Porsche garage.
Here are the ranges for 997 GT3:
Range 1 : 8400-9200
Range 2 : 9200-9400
Range 3 : 9400-9600
Range 4 : 9600-10.000
Range 5 : 10.000-11.000
Range 6 : >11.000
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M3 CSL / Alpina D3 Bi-Turbo Touring / RS2 Avant / GT3RS Kermit