There have been times in the past at the launch of an all-new BMW 5-series when we have questioned the merit of tests such as this. We've always gone ahead with them because you cannot prejudge such encounters, but since at least the launch of the E34 5-series back in 1987, the result has always gone the same way. Five meets Mercedes E-class, Five beats Mercedes E-class, Five goes home. That's 23 years of fairly foregone conclusions.
BMW has run out of E numbers now, so this generation is called F10, but it wasn't so much anything about the 5-series that made us relish this particular contest more than any similar encounter in the past two decades; it was something about the E-class. Before either squared up in the Portuguese sunshine, we didn't merely suspect that this would be the toughest fight of the Five's life; we near enough knew it.
Never has the E-class stood so proud of its class as this one does today. It has already pasted the outgoing 5-series, a car for which we have no shortage of affection, and dusted the Jaguar XF. Moreover, it's never better than when fitted with Mercedes' 3.0-liter diesel motor, precisely the weapon we have lined up to take on the 530d, historically the best of the basic 5-series.
No longer will it be good enough for the Five merely to be more fun than the E-class, because the Mercedes has come on so far in so many other areas; the BMW must compete on all fronts. It will need ride and refinement unapproached by any predecessor, a proper rear seat package and huge improvements in quality, both perceived and real.
If it also retains all of its hitherto unrivaled capacity for driving pleasure, then it might lay credible claim to its once-assumed class dominance. Otherwise this story may have a rather different ending from all previous confrontations.
Both cars look disappointing. The Mercedes is odd, the BMW just bland and unimaginative, as if the company started to retreat from the oft-criticized Chris Bangle school of edgy design and didn't know when to stop. In the metal it has little presence, though that's probably preferable to the Merc, whose considerable presence serves only to remind you how unattractive it is, especially around the nose.
Inside the 530d, BMW has made useful progress, and whether its cabin is preferable to its rival's depends on your priorities. Certainly it works better; its switchgear is more lucidly arranged, its dials are clearer, the new iDrive controller clearly superior to Mercedes' rival Comand system. There's a clean, airy feel to the driving environment, backed by a flawless driving position and excellent visibility.
What it lacks is a sense of occasion. For all its efficacy, this is not the cabin of a luxury car, whereas that of the Mercedes undoubtedly is. Less coherent is may be, but the way the E-class deploys its wood and leather and subtle but extensive use of chrome has a class missing from the BMW.
The Mercedes is also going to make better friends with those who elect to travel in the back, but no longer by much. The real news is how close the BMW now comes to offering E-class interior space. In neither car will any less than the freakishly tall be troubled for head room, and for once the E-class's advantage on leg room has been much reduced. Indeed, for the first time in its 28-year history, the Five can claim at last to seat four large adults in comfort. Its trunk is fractionally smaller.
But what you really want to know is, which car is better to drive. And the perhaps surprising answer is that this is an extremely close-run contest, determined by nuances here and there and a presumed order of priority that some customers may not share. BMW, whose supremacy in this area is measurable in decades, would be correct to be concerned by this.
Most importantly, both are fine cars to drive fast or slow, in a straight line or through some corners. The paper advantage belongs entirely to the BMW, which offers a little more power and markedly better acceleration, whether you choose the standard six-speed manual (and make your car difficult to sell), or join the other 95 percent who will choose the optional eight-speed auto fitted to the test car.
This new gearbox works brilliantly, better than the six-speed auto it replaces and the seven-speed unit used by Mercedes. Somehow, it seems always to be in the right gear without perpetually hunting around for the optimum ratio. It knows exactly when to change down and when to keep its nose out of the engine's business and let the torque do the work.