My view is you'll have to test drive one.
Let me put it this way, my father has an Aston Martin DB9 but once he test drove the Nissan 370z, he actually preferred the Nissan over his Aston. I'd agree with him, after driving both, the Nissan lacks the awesome supercar power that the Aston has but it's just MUCH more fun to drive and there's no squeaking or rattling (unlike Aston).
More to the point, I'd say comparing with your car, yours would be the overall better car for things such as for motorway driving but the Z will be more fun to drive for a quick spin.
My neighbour has a BMW 335i which sounds great & prolly drives great but it's no M3, it's quite boring to look at. Once I get my Z, it'll be parked right next to his Beemer ... muhahahahahahahhahaha
