I know this isn't an easy thing to do, but just for now let's ignore the BMW M5. If you're not interested in that car's startling performance - or are not prepared to deal with the compromises which result from it - there is a strong case for saying that the 535d is the ultimate 5-Series.Even if you don't count the M5, the 535d is not the fastest car in the range, nor is it the most expensive. And it has stiff competition from within its own stable, supplied by the 540i and the 550i.But those are petrol cars, and the 535d is a diesel. Its three-litre, six-cylinder, twin-turbo engine is rightly regarded as one of the best in the industry. Its maximum power output is 286bhp, which would have seemed like either a typing error or a ridiculously optimistic figure just a few years ago, though it's less than either the 540i or 550i can manage.Like those cars, though, the 535d can go faster than its limited 155mph top speed. Its 0-62mph time of 6.4 seconds is not far short of what the 540i can manage, and although the 550i is a second quicker it uses vastly more fuel. And in any case, 0-62mph times - which don't relate closely to anything you're likely to do on the public road on a regular basis - are not friendly to diesels; it's how the car performs while it's already moving that matters, and there can be no complaints about the 535d on that score. This is a car which, to say the least of it, is quick enough.The diesel engine is one of many to have benefitted recently from BMW's new EfficientDynamics programme. The cleverest part of this in the 535d is the Intelligent Alternator Control with Brake Energy Regeneration system. To tell the tale simply, the 535d recharges its battery partly through energy recovered during braking and coasting, and the alternator is activated only when needed, which improves performance, fuel economy and CO2 emissions. A win-win-win situation, then.One result of all that is that this large executive car has an official combined fuel consumption figure of over 40mpg. That's impressive in itself, but more so because the 535d is also so quick.Nimble, too. I'm prepared to admit that, on a dry road, I set the traction control warning light flashing a couple of times. I'm less ready to explain what I was doing to make that happen. The point is that the superbly crafted rear end of the 5-Series can deal with 286bhp - and with shovelfuls of torque - without seeming in any way concerned about it.In fact, occupants can feel more stressed than the car does. BMW people quietly admit that the company went the wrong way with ride quality a few years ago, and things are definitely improving, but the 535d (in M Sport form at least) still needs work. It's too jittery, too fussy, and that's a shame considering how comfortable the car is in other respects.As with all other 5-Series models, there is a huge amount of room for passengers at either end, and the seats are splendidly comfortable and supportive. As of the 2007 model year, the driver of a six-speed automatic version (and there is no other kind of 535d) gets a restyled gearlever which, frankly, looks bizarre but sits nicely under the hand.The exterior styling, which drew so much adverse criticism when it was first shown, is not as shocking as it once was, though I have to say I still don't find it attractive. The interior is better, but I don't think the test car's Black Dakota leather upholstery did it any favours. This isn't very black at all - more a dark grey, really - and personally I think it cheapens the look of the interior. If it were my £42,000-plus on the line I think I'd choose a colour that did a better job of reflecting the price.The 535d M Sport is well-equipped as standard. The list price includes Dynamics Stability Control, air-conditioning, cruise control, floor mats (often listed as a £75 option in lesser BMWs) and the effective but still complicated iDrive system which looks after the heating, audio, navigation and communication systems.BMWs offered to the press are often fitted with enough options to add a considerable percentage to the basic price. In this case the "extras" total came to £2475, which doesn't seem so bad when you're paying over £42,000 to start with. The most important option was the set of rear side airbags (£230), the cleverest the lane departure warning system (£350), the most expensive the xenon headlights (£720) and the most annoying the sliding front armrest (£130) - can't they just include that as standard?For a further £280 you can also specify DAB digital radio, which is brilliant when you can get the reception. When you can't you can just switch back to FM (or even AM, if you still bother with that) as normal.I didn't fall in love with the 535d M Sport, but I was impressed by it. It's smooth, fast, relatively economical and brilliant to drive. With a different interior colour and a smoother ride I could be seriously smitten. Engine 2993 cc, 6 cylinders Power 286 bhp @4400 rpm Torque 428 ib/ft @1750 rpm Transmission 6 speed semi-auto Fuel/CO2 41.5 mpg / 182 g/km Acceleration 0-62mph: 6.4sec Top speed 155 mph Price From £42591.00 approx Release date 24/03/2007