I've driven quite a few of the cars at Prestwold, including a GT-R.
I have found the instructors to be very good, as long as you show that you are listening to them and give them confidence that you do what they say, then they let you push the cars a little.
The GT-R is so fast it's funny, but I felt like more of a driving hero (even though I'm not) in some of the other cars, so I don't think I would choose to own one, personally. Glad I drove it though.