I can report some details, as we have both cars in the family. Yesterday we tried both cars on a circuit in my home region of Styria, Austria. I use the same circuit for all cars that I try out. The results do not show everyday economy. They are just for comparison. The country is hilly, the height difference of the 10,5 miles circuit is 300 ft. We drove the circuit yesterday with both cars with roughly the same speeds. The battery level at the beginning and at the end were about the same, too. Both engines had been warmed up before the test. The top speeds were 56 mph, in villages 32 mph. The result: Prius III 3.3 liters per 100 km (71 mpg). Prius Four, not IV after MY 2010 2.5 liters per 100 km (94 mpg).
So even allowing, say, 10% loss of efficiency for the Prius III, that is still a great improvement. I haven't had my Prius Four,. not IV, long enough to reach each any conclusion about l/100km but it definitely seems much more responsive and snappier (in ECO mode)
I agree. The new one is more responsive. I still like the Prius III, too. It's my best car so far. And the Prius Four, not IV, is two levels better (it's my son's new car). Before I had a Mercedes, 2 VWs, an Audi and a Porsche. The Prius is way better than any of these. Well, maybe the Porsche (which I still own) is a nice toy, too.
By the way, the consumption values of the Prius III (shown on the dash) are a tad optimistic; well, that's the same with many other cars. The difference between the predicted average consumption and the real values computed at the petrol station is in the ballpark of 0.25 l/100 km. The same thing with the Prius IV, I admit. But only by about 0.1 l/100 km. So, in comparison, the Prius IV dash figures are a bit more honest than that of many of its competitors.
Btw, In the meantime I have even managed to achieve 2.2 litres / 100 km with the Prius IV on my 10.5 miles circuit. The Prius III does it 2.7 litres. Both Prius cars are NO Plug-in types but ordinary Priuses. I can say that the battery charge level after the ride is the same as at the start, so the figures are no fake.
stupid replying to a 2016 thread, but no one posted the differences between the two that would account for the mpg differences.