Ya everyone explained it already. The extra weight of the GS, plus you and your girlfriend, is probably 400+ pounds more. That will slow you down quite a bit. Even with my gf that is about 100 lbs in the car, it slowed me down 0.2 seconds in the quarter mile. I would image you would be about 0.5 to 1 second slower than a RS if you had an extra 500 pounds of weight. Plus the akimoto intake an exhaust probably gave you around 10 hp at most. That would only make a 0.2 second increase in quarter mile time probably. Either go turbo, nos, or just go for "show" so you can look fast hehe.