i have the 6000mah 25c 5s(2+3) in my savage xl flux and its plenty, so in normal car setups there is no need for 45c(thouh this depend on the pack size and power demand) with nano 6000 mah the runtime is so long that in the end its almost boring.

in my truggy i use nano 6s 5000 45c (and normal turnigy 30c), those hardcore racers often use a smaller pack like 45c 3000mha becouse of weight