The GS definitely is faster, but I will say that my 01 Intrepid ES handles FAR better.
I was torn between buying a 300M vs a GS but the GS has more options, more luxuries, more power, easy engine to modify for cheap, but handling is worse.
I test drove both a 300M and a GS on the highway and I will say this.. the GS really surprised me. At highway speeds the engine isn't even working..it's at like 1500mRPM or lower, and when you punch it from 60mph it literally just goes, zero hesitation just pushes you back, all that torque is very very fun and is what basically sold me on the car over the handling issues vs the 300M which handles much better, although to me the GS response is more like a V8 than a V6, and the most important thing for me in buying was the power. I can see why some would rather the 300M or R/T trep though after having driven both.