You will notice a BIG difference. It will let you put another 10% torque to the ground! And that is just the difference of the diff. Just make sure that you get the speedometer gear that matches the diff or else your speedo will read faster than you are actually traveling. It sounds like you're getting the trans/diff from the same car. If so the speedo gear you need is already in the tranny. You could probably knock 1 sec off your 0-60 depending on how stock your Z is.
Good luck! and enjoy!