I don't get it, Pete: it is not the fuel that goes in which is interesting but the power it makes.
Fuel economy also creeps into the picture when a tanc of fuel is empty after half an hour of madness unless sitting on 200 l (= 200 UKP) of easily burning petrol is an option.
Let's throw a big rock in the pool... what's best: a 700 Hp Ultima using american beast doing 3MPG or a 400 Hp V8 TDI audi-Ultima, thundering - hunning is a better word-at 3800 RPM and 270 kph for hours?
Nope: it wasn't an Ultima nor a Porsche who did Brussels Muninch (880 km) in 4 Hr 12 min without refuelling... if I needed to do that with a (slightly tuned) 928 I would need the RAF for refuelling when on the go and still it would be a hell of a close call.
Petrol engines are only usefull when weight comes into the equation: Lotus Seven/ Elise-style but once you have a car weighing above 1500 kg, the engine is diesel, my friend.
Second rock: if your turbo-rangie sported 300 HP and a (turbo)-diesel engine you would be swarmed by potential buyers. It being a petrol engine, makes it a bit less interesting, doesn't it? Even Arabs, drilling their own oil, aren't interested,as they have the money to buy new toys.
Tom De Moor