I have a 2011 GTCS... mine came with 3:55 right from factory and love them,a friend of mine also has a 2011 GT with 3:73,both our cars are 6 speed manual trans
He checked mine out heading up to my cottage,and I drove his,( lol so we switched cars WITH wifes inside ) that was a game changer for him,he is installing 3:55 in his this winter.
His comments: "your 1st 2nd gears are usable compared to mine,I barely move in 1st/ and I gotta shift... he also noticed that @ 120 km/hr my engine is just around 1700 rpm, he tells me up top his seems to be reving way higher than mine (duh) lol.
My comments on his;
Useless first gear,but more potent,easier to break tires loose ( I much rather put the power to the ground than loose it to wheel spin) second gear on his scrembles to red line faster,where as mine seem way taller.
His complaint is the gas milage compared to mine,both filled up at a Shell with 91 premium... when we got there,my gauge had barely moved ( 120 km distance to my cottage) mine was right between full and the 1st quarter... his was between 1st quarter and half full.
I enjoyed driving his,felt nice,but tires need to be wider/stickier to tame wheel spin...I can easily spin mine out as well, but seem to hook up better with stock tires.His worst complaint is city driving and gas usage.
These are seat of my pants observations as we switched rides.Personally I'm very happy with the 3:55, if I had to do it again, I'd still stick with 3:55's,but that's my opinion!