The GT2 RS is a 2011 model in the U.S. There was no "RS" before that in the U.S, only the GT2.
The Porsche 911 Turbo S is only built now and then. The last times Porsche built the Turbo S corresponded with the ends of the 993, the 996, and the 997-body forms of the 911: the 1997 911 Turbo S (air cooled with 424 HP and 400 lb-ft torque), the 2005 Turbo S (water cooled with 444 HP and 457 lb-ft torque), and the 2011 911 Turbo S (water cooled with 530 HP and 516 lb -ft torque). I think we can expect the next Turbo S in about 2015 to 2017.
While the Turbo S is faster 'off the line' than the rear-drive GT2 RS, the GT2 has a higher top speed, weighs hundreds of pounds less than the all-wheel drive Turbo S, and is quicker than the Turbo S around most road courses, if a consummate driver is at the wheel.