I'll try to clear up a few things here.
First off, I don't know anyone who has taken their JX or QX60 to the track yet, so it's kind of hard to answer young padwan's question. My butt meter says the QX60 may be slightly faster in initial acceleration than the original JX35.
As for the tranny - back around May Infiniti made a mid-year change to the transmission in the JX35. So any JX built after that, and all QX60's, have the new transmission. No one from the factory has stated unequivocally that it's the transmission from the Pathfinder, but that seems to be the sense from everyone. That said, I've not seen any problems from any JX or QX60 customers regarding the transmissions on their vehicles.
If I'm not mistaken, the initial PF vs JX test drives by Car and Driver showed the PF with 1/2 second faster on 0-60 and 2/10 of a second faster on the 1/4 mile. It was due to the regearing. Added 7th gear lowering the ratio on the 1st gear for the boot in towing. I say gearing, but you know what I mean. The times were not that different.
As for no problems with the tranny's, that is not correct. The there a multitude of problems with the PF tranny and some of the JXs produced with the new tranny after March 2013. The shuddering issues is fully known and has now been recognized by Nissan. Feel free to reference any PF forum for examples.
Please reference TSB ITB13-20a regarding the VIN range for this TSB. Keep in mind that this TSB has been revised a third time. Nissan has acknowledged that the shudder is not one thing but one of three different items that can be causing the shuddering. The TSB has not been publicly posted yet, but it does reference hooking up a computer the car and driving for 30 mins. The computer then tells the tech what the issue is that is causing the problem. I believe the issue could be a computer update, the torque converter, the solenoids, or the valve body, if I'm not mistaken.
JATCO has apparently begun pulling the new tranny and swapping out all three parts, relabeling them as Remanufactured and doing full tranny swaps on JXs and PFs. Pretty sure if your QX60 was built on 07/13, you should be okay.
Hopefully, no on here has had the issue or is out side the VIN range.
Since SINECURE works for a dealer, maybe he'd be so kind to get a copy of the TSB and post it for us.