It's not exactly laughable. They are pretty quick cars.
I test drove one a couple weeks ago and
almost traded my GT in and leased one. I would have it now if not for the fact that a 20,000 mile lease requires you to pretty much almost pay full value of the car only to give it back...so i walked.
But anyway, slow off the line but from a roll they can move well. From a dead stop race the Mustang would have the advantage with torque. From a dig on the highway it will hang with a stock GT....I had the pleasure of finding this out firsthand when a '08 G35x played around with me on the highway and was right with me at my every move.
The 6-spd RWD version is supposedly quicker and guys on G35driver.com where i hang out are getting mid 13's out of them. The AWD G35x is able to hit a high 13 stock, but only a few guys have gotten a 13 second time slip from the AWD model..they are typically a low to mid 14 second car. They are posting timeslips and vid as well to back these times up. It's almost scary how easy a 13-second time slip can be had with one of them with a few mods. There are several in the 12's with bolt-ons.
Now go to the track and watch how many 99+ are struggling in the mid 14's even with minor mods
Honestly, i was all set to trade my GT in and felt like i was staying even in the speed department...but gaining one hell of a car.
As soon as I sell my GT privately, i am going down to talk about purchasing one. It's not going to stay stock either

I love G35's