sir the best mileage i ever got from my prius is 30 km/l equal to almost 70mpg i have a snap shot of it i will post it to support my say, sir it might be true that uk model prius has smaller radiator but i havent ever faced any overheating issue car has seen many harsh hot weather conditions of lhr multan in july aug with full time ac on , sir about your third quiery i can say this a prius can outrun a civic till 100 but both should be auto after that civic takes lead i have tested this on my own civic as well as with some other frnds the results were same , though manual civic is faster , this is a fact , sir about battery let me tell this is an important thing that we should know , battery charging and drainge time are different in different atmospheric conditions , winters it gets charged quickely where as in summers it takes time to reach the same amount of charge , in terms of distance a battery should charge to max blue with in 1 to 1.5 km on normal driving , a full green charged battery can be driven almost 4 to 6 km on ev mode with very light foot as if you floor it the petrol engine will itself kick in
abt your last inquirey maximum speed that can be acheived on total battery depends upon the level of charge my prius goes upto 70km/h when battery is fully charged till green and 55 km/h on blue indicator of charge
hope i satisfy your concerns
any other questions are welcomed
regards ,