As far as I understand the differences in US GT3s are that:
1. Sunroof is standard (unfortunately)
2. You get cruise control as standard
3. You get TPM as standard
4. You can't get the Carbon (CGT style) buckets due to lack of airbags (US DOT regulations)
5. And for this reason you can't get the Club Sport option (unfortunately)
6. But you pay 35% less...