The first thing to note is that even the baby 2.2 has a six-cylinder engine in its nose, so the last thing it feels like is some sort of basic model whose sole purpose is to prop up the tail-end of the Z4 pricelist (unlike the previous Z3 range).

That 2.2-litre engine is super creamy, effortlessly spinning close to 7000rpm with a typical BMW howl, but somehow lacking any sort of power rush along the way, or a decent dose of torque for that matter. In fact jumping from the 2.2 into our long-termer had me nearly through the car park fence, such was the difference in step-off.

BMW has tried to disguise this power deficit by fitting a lower final drive in the 2.2, together with a five- rather than six-speed 'box, so the engine is constantly spinning higher up the rev-range for any given speed (which doesn't help fuel economy either, as the 2.2 seemed to drink just as much as its larger-engined brothers).

This constant need to row the car along should make it great fun, as the gearchange remains terrific, but somehow the driving experience comes over as being a bit flat, chiefly because the chassis is never particularly tested at any point.

The extra power and torque of the 2.5-litre make that car a lot more rewarding to drive and well worth the extra ΂£2500 BMW charges over the 2.2. Its larger power output also gave the chassis more of a workout. Unfortunately our test car came with the big optional 18in split-rim wheels (and run-flat tyres) which look terrific but kill the ride quality stone dead. This 2.5 felt just as bad as our 3-litre in this respect.

The additional ΂£4200 needed to buy the 3-litre Z4 over the 2.5 gets you air-con, electric seats, leather trim, six-speed gearbox and the dreaded sports suspension as standard. Fortunately it also buys you one of the world's greatest engines; effortlessly quick, torquey, economical and well worth the extra money BMW charges.