This may have been the one car that replaced the "standard" GT2. The 997.2 lineup was quite tricky, especially as far as the GT lineup went. You had your Carrera GTS, then the GT3, then the GT3 RS, then the GT3 RS 4.0, and finally the GT2 RS (in terms of segment).
Carrera GTS = level 1 track-focused supercar = Grand Sport (C6)
GT3 = level 2 = Z06
GT3 RS = level 3 = Z06 Carbon Edition
GT3 RS 4.0 = level 4 (raw power) = Z06 Z07
GT2 RS = level 4 (grand touring) = ZR1
Technically, both the 3RS 4.0 and the 2RS are level 4; the same with Z06-7 and ZR1. However, the 2RS and ZR1 tend to prioritize straight-line performance over downforce and tight cornering. The standard GT2 (from the 997.1 generation) was both a raw-power vehicle as well as a grand-touring type of vehicle, so it did ingrain a little bit of Z06 and somewhat influenced the ZR1.
Had there not been a Cayman model, the Carrera GTS would possibly be called a GT4. However, the Cayman R was the precursor to the GT4 and GT4 RS models. Porsche did not race in GT4 at the time, but the Cayman R was sort of a GT3-lite. The 987 Cayman is not a C6 Corvette competitor, but a 370Z/S2000 competitor. The "R" version competed against the NISMO and Club Racer versions of those cars, as well as Lotus.
Today, the GT3 RS and the GT2 RS (which is still soon to come) are in the same exact segment, as proven by the 991 and especially the 992 generations; both can easily be considered GT2 (Maserati even used the current GT3 RS as the benchmark for their "GT2"-version MC20). Likewise, the Z06 and ZR1 were starting to get much closer than ever with the C7 generation (the ZR1 was really supposed to be ditched away entirely, with the Z07 package becoming more mainstream for the Z06 to act as some sort of "new ZR1", but the new actual ZR1 version was released at the last minute anyway); the C8 generation shows that the ZR1 is a twin-turbocharged version of the Z06 with very mean hood vents (everything else about the ZR1 is the same as that of the Z06).
Edit: Now compared with things like a Turbo, Turbo S, SLR McLaren, SL65 (or SLS) AMG Black Series, 599 GTB Fiorano or even GTO; these things are spiritually (and more logically) muscle cars.
Think of these as like the supercar versions of the Shelby GT500KR and Vauxhall Monaro VXR500 of that era. There is almost no luxury in either of these two (3RS 4.0, Z06-7). It's all row your gear, brutish power, subtle prestige/status (relative to standalone exotic cars), and that's it.
