Having built its reputation on developing small and agile sports cars, Porsche has diversified and broadened the brand's appeal with the SUV Cayenne and executive five door hatchback Panamera series.Now those of a certain age will remember the Porsche 928 of the 1980s and to me the Panamera is a natural successor. It is a modern version which sets a new benchmark for executive saloons/hatches without diluting the driving dynamics so familiar to Porsche owners who may now want a genuine four-seater.There are seven versions in the Panamera series sold in Britain. They share the same four-door + tailgate, four-seat body and are priced between £61,400 and £97,400.Depending on choice of 400 and 500 bhp V8 or 300bhp V6 petrol engines you can have rear or four-wheel-drive versions with 6-speed manual or 7-speed automatic sequential transmission systems.To my mind if you want the full benefit of the model you must go for the S4 4x4 I tested. In ten months of 2010, Porsche GB sold nearly 700 Panamera models and 40 per cent were the S and 4S versions.The first impression of the Panamera 4S is that it is a big car, measuring 4.9 metres long and 1.9 metres wide and it has been carefully styled to incorporate design cues from the 911 and Cayenne series. Open the doors and their lightweight feel may surprise you but also gives a clue to its power to weight performance advantage. Engine and drivingThe Panamera 4S uses a V8 4.8 litre petrol engine and seven speed sequential automatic powertrain with permanent four-wheel-drive.It is a truly awesome package not only because it gives instant strong power with incredible smoothness but it can return reasonable economy for what you get, incorporating some clever fuel saving technology, most notably its automatic stop and start system when idling which is part of the PDK energy capture package.On the move, the creamy smooth changes up or down the box under part or full throttle are highly refined and you are never left hunting for a gear to accelerate, and you have fingertip spoke-rockers or can move the lever manually to exploit the desired ratio.The well weighted smooth throttle is matched by the precision and feed-back from the footbrake. It slows the Panamera 4S very quickly, with absolute control, no drama and no need to push hard to bring about a dramatic stop.Turning to the steering, the Panamera's system is finely balanced with reassuring weight at speed and easy ability to turn in a tight space when parking or manoeuvring slowly in town. There is no vibration or kick-back and it is arrow-like at speed.You can hear the big wheels and tyres on coarse surfaces but, surprisingly, there is do deviation due to their size and with remarkable compliance in the suspension the Panamera soaked up really bad bumps and potholes with notable smoothness and without letting anything be felt inside.At the other extreme, the roadholding was tenacious on any surface, the handling was near neutral and it was never thrown off line by mid-corner bumps. Despite its size, Porsche has done a good job in keeping weight down to about 1.8 tonnes and it felt remarkably agile as a result.Secondary controls are very closely grouped around the column, wheel and the driving position so everything is immediately to hand even if the proliferation of similarly shaped buttons on the centre console needs familiarisation to get right first time, every time. Instruments are reasonably sized and very clear directly infront of the driver.Near silent wipers clear the screen very effectively, the headlights are extremely powerful and far reaching and the visibility is better than I expected from its coupe profile, although you do have a blind-spot over the shoulder when pulling into traffic. Interior and refinementFor a coupe it is very roomy in the back. Access is good, the front pair of seats have plenty of adjustment and all hold occupants very securely and are notably supporting. It is worth highlighting the easy loading luggage area increases from 445 to 1,263 litres, but it's not a very deep compartment.Silence is golden, and in the Panamera it is particularly outstanding. Doors close with a gentle 'whomph', the wipers do not make any noise when working and there is little mechanical intrusion from the powertrain. You can hear the tyres over the road but suspension rumbles are very low by comparison. Open up and the engine note becomes more noticeable but it is a pleasant sound.The thought and care so evident in the Panamera's design and build means it is a very refined and sophisticated grand tourer in the 4S version as tested.I would take issue with those who say it is a four-door 911. It is a different member of the family tree and to me its roots lie in the 928.The Panamera 4S does all that the 928 did, but very much better and with greater performance and practicality for today's world of supercars. It not only upholds Porsche's reputation, it extends it. Porsche Panamera MILESTONES Porsche Panamera 4.8 V8 4S PDK 5-Door Coupe/HatchPrice: £78,938Engine/transmission: 4.8-litre V8 petrol 400bhp 369lb ft of torque, 7-speed automaticPerformance: 175mph, 0-62mph 5.0 seconds; combined cycle MPG 25.4mpg, CO2 260g/km; VED road tax £950 at first year rate then £435 a year; BIK company car tax liability 35%Insurance group: 20/49For: Fast, practical, stunning to drive, brilliant handling, refined and classyAgainst: Expensive for what it is and very costly to run, rear quarter blind spots, shallow boot