Bleah... i posted that green GT3 RS before when it was parked
right outside the city showroom... no one said anything. then this
sand king post it again parked elsewhere, u all like wahhh woooo
wow 
anyway, the GT3 is based on the Carrera S, with a more powerful NA
engine.
GT3 RS is the same as the standard GT3, just lighter and plus some
"GT3 RS" sticker. 
the current GT2 is based on the 996 Turbo chassis with the same
twin turbo engine , with slightly higher power output than the
standard Turbo and it's RWD, unlike the Turbo's 4WD.