Thinking about the Z3's cornering ability, I do not believe it is as simple as blaming the antiquated suspension design. Many drivers today learn to drive in front wheel drive cars, which will always react differently around corners than rear wheel drive cars. /
Cars that are rear wheel drive need to be set up perfectly to take a corner at speed. the speed at which they can take the corner depends on three things:- The line taken from the approach to the corner, selecting the correct gear for the corner and balancing the car on the throttle through the corner.
Front wheel drive cars are far more forgiving in this respect, even a car with an antiquated suspension set up, if rear wheel drive, can be made to take a corner fast. :-ss
The question of whether a Porshe Boxter is faster round corners than any Z3, will depend on a large part on the ability of the driver. Whatever rear wheel drive you are in, if driven incorrectly through the bends, will wallow and roll if the proper technique isn't applied. This is why powerful cars like Porshes and Jaguars can some times appear to be out performed by Mini Coopers. B-)
The lesson was brought home to me many years ago, whilst watching minis race a Ford Thunderbird at Snetterton Circuit. The T'bird could only use it's power on the straight and would always open the gap on the pursuing Mini, however by the time the T'bird was exiting the S bends at the bottom of the straight, the mini had caught up again. The eventually winner of the race however, was a well driven Ford Anglia, which although under powered, was driven superbly and managed to maintain a lead,