I wouldnt give up the gas mileage , with the transmissions in the newer cars I doubt it will provide the gain you are looking forWow! This section needs CPR and a defibrilator!
I'm a few months from a new car but I may just buy those 4.30s and stash them under the bed in preperation for my 2012.
My wifes 06 V6 has a 8.8 with 4.10s and a 5A trans and feels like a GT if you lock out the OD and leaved it in d3. I'm pretty sure the 305 HP and nearly zero torque at low RPMs will really exploit the 4.30s. No opinions???