Sam - don't worry, So what if a car can turn 90 degree corners quickly?
Nobody drives like that.. the most fun cars are ALWAYS the ones with sensible levels of grip working in unison with the chassis, suspension and you to put a big smile
on your face.
Fun exists in finding and playing at the limits of your car, (easier done and more controllable if they are lower), not yanking the wheel round a 90 degree turn.
Oversized wide wheels and low-profile tyres will increase tramlining, reduce bump absorption and reduce stability over all but the smoothest of roads.
Point out the notoriously wobbly rear suspension of your friends E30 BMW 3-series and direct him to some European car magazines about it, if he's giving you 'ultimate driving machine' cr*p. It's the same suspension they put in the Z3, and the reason it is so hated by enthusiasts.
later
Russ