I have recently taken delivery of the Mazda6 150ps and at the first fill up it achieved 43 on the pumps and 42.9 on the car computer. It is now showing 48 mpg on the car computer. My driving is a mix of short runs in the town and 60 mile round trip motorway driving. I am happy with the car so far.
There was a report on the internet recently about the manufacturers claims of fuel consumption and the test they use to arrive by that, which is nothing like normal driving. They then remove ( or not supply) the spare tyre (claim this prevents low emissions and low economy) , tape up door joints, do not use any accessories like a/c, heater, lights etc. They then claim that you can buy a tyre and jack as an extra.
I suppose these figures that manufacturers use if compared with each other are just a guide, but may or not be achievable. It all depends on how you drive and how much rubbish you carry in your boot, do you garage it (keeping it that much warmer) thus shorter time to warm up (extra fueling) in the winter. Don't run the engine on idle in winter( to warm it up), but drive off straight away, but gently as more wear takes place when the engine is cold, more fuel dilution of the oil as the pistons, rings and cylinders have not come up to normal temperature.
Though I have noticed with the Mazda the temp light has gone from blue to blank in less than 3/4 of a mile helped by the recirculation of exhaust gasses. I would have preferred a proper temperature gauge though with real temperatures on, particularly if you have a chance of overheating in some conditions.
My previous car a 14 year old R45 did achieve some of the figures the manufacture claimed, in fact my Urban was much better than mfrs, even in the winter.