All the GT 0-60 testing I've seen shows the AWD and RWD pretty much identical. The AWD has more grip but is slightly heavier where the RWD has less grip but is lighter.
Another thing to consider is that 0-60 times will be affected by lots of factors including ambient temperature, humidity, road surface, wind speed and direction, even how much gas is in the tank which would change the total weight.
I think it's cool that these folks are getting the 4.5 sec 0-60. Every reliable/ professional time I've seen is in the 4.5-4.7 second range.
The car is definitely fast.