The best I've seen out of my underpowered small diesel van is 45MPG. Poor. It is constantly thrashed however and running on veg.
I'd call that a win still - you're effectively paying less for more fuel.
Let me see what my fleet's like round the doors:
All time record in my C4 (before the engine shat its bottom end) was 59.5mpg. All time record distance on a tank was 803 miles. Average was 48-50mpg, poor was during the summer on a film set 5 up when I got 43mpg, record low was 11mpg driving flat out around Castle Combe with the air con on.
Amazon was dog shit dismal with its microclimate total loss oiling system - though it was a damn sight more reliable than it is now. I reckon between 16-18mpg was what it was managing. The refreshed engine won't fucking well run for long enough for me to actually measure mileage; every time I take it out it breaks down.
Leon only has 20k on the clock so I reckon the engine's still tight. Everyone else seems to be able to piss 70mpg from these engines; I average between 65-68mpg.
960 does 26-27mpg, which is solid given its weight, ceefax aerodynamics, carrying capacity and 4 speed autobox.
Piazza is currently managing between 30 and 33mpg on high octane pez, which is astonishing considering it's nearly done 160k and recorded test figures BITD of 21-22mpg. I swear 80s fuel was mostly wee and resentment.
605 diesel hovered between 43 and 45mpg. I will have another 605TD which isn't made of despair and pigeon diahorrea welding one day.
305 Auto: between 28-30mpg consistently.
Knob_van: 40-42mpg, although Captain Slow got a bit more out of it. I suspect the Rallye wheels and tyres are gearing it up a bit.
MGF VVC: between 31 and 35; most people with 'Fs get more but I doubt very much that they thrashed the living shit out of their cars like I do. THE NOISE, etc.
SVX: never brimmed the tank before the gearbox checked out; I doubt it'll do more than 25mpg given that it has a 3.3-litre flat six, permanent 4WD, a dry kerb weight of 1620kg (nearly 200 key more than the 960, which was way lighter than what I expected) and a mard slushbox. I don't care, mind.
Xedos was way better than expected, managing 31-33mpg even if belted. MX-3 was savagely crap given its performance: 27-28mpg was all it did.