The Z4 is a good car and we haven't heard of any issues with the steering or handling. In terms of rear-wheel drive convertibles the BMW 3-Series Convertible is a great choice too (although larger), and if you're after power the 330i models are superb. For something with genuine performance, there's also the Jaguar XK8 and XKR, or alternatively you could consider a Porsche Boxster. In terms of buying, the best time is usually November through to February.