RC:
the GT2 RS is a great product, it really hasn't the same track capability the RS 4.0 has.
but then: the GT2 is faster around the NBR, is faster around HHR, is faster around probaly any other track, is faster on the straight... I.e. on each and every objective criterion the GT2 is the more efficient / faster sports car
P.S.: Just did a little sample calculation
if you compare GT3RS, GT3RS4.0 and GT2RS the hp figures are
450, 500 and 620hp.
I would speculate that the lap times of the three cars are approximately linear to the hp figures - looking at the officially claimed NBR times:
7.33 (SportAuto), 7.27 (official claim), 7.18 (official claim)
Thus, based on these considerations all three cars (including the "normal" GT3RS) should have very similar track capabilities, their performance is primarily driven by the different engines...