1st off, welcome to the site.
In regards to the car swap the bmw will be a big drop in HP but it should still be a fantastic car to drive, they are great at handling and probably better in respect to the z28. It will probably not go in a straight line as fast but they are very fun to drive. I would suggest test driving the BMW and see where it goes from there, and as we are a BMW forum we might all be more partial to the BMW.
Good luck with you decision and let us know if you have any questions.