Hello Blubyu, I don't think the gears have much to do with the comparable performance of the 10 GT and the 11 GT since both are auto tranny cars. However, I am not sure what the gearing in the 6 spd auto tranny is in the 11 GT compared to the 5 spd auto in your 10 GT. Were you able to drive the 11 GT on the highway above 3,500 RPM's all the way up to around 6,000 RPM's? I have driven both cars (10 & 11 GT's with auto) and I can tell you the 11 GT is quicker due obviously to at least an additional 97 HP and 65 lb-ft of additional torque. I guarantee you (stock vs stock) the 2011 GT is quicker and will trap at a much higher speed than a 201 GT.
I also believe the car is just not all about speed. Which I do LOVE speed trust me on this one! I also believe this new 2011 GT 5.0 is not only the smoothest, quietest, best handling, most responsive car I have ever driven and I have owned three Shelby Mustang's as well. You cannot go wrong with this car IMO. I wish you the VERY best with your decision and I hope my experience(s) helps you. Take care and please post pics when you buy your new baby! Jack