The 7AT is quite good. I use my Z as a DD so the auto is quite nice to have. No issues with spirited driving and kicking the rear end out with the 7AT. I'm learning how to use it better now as I have 5k miles on the car at this point.
There is a slight delay when you jump on the gas vs. a 6MT, but you can work around it. When you put the car in "D" it drives and shifts smooth as butter and when you put it in manual mode it's still a blast to drive.
No regrets but if you are not using the Z as a DD and just a weekend toy, get the 6MT as it can allow for a more connected feel and is a bit more fun.
Oh and I agree with someone else who posted...having a 6MT makes it easier to tell the ladies they can't drive the car.