Have not taken the G8 to the track yet but from the times I have seen the Duramax is faster.
0-60 the Duramax is definitely faster but this G8 has some long legs with the 2.92 axle gears it pulls up top like crazy the duramax starts losing steam trying to push itself through the air and this car comes into its stride
100 mph in the g8 feels like 50 in the truck it is very smooth and stable