150 bhp in a car that light would be exceptionally quick, probably sub 7 seconds, depending on the number of gears you need to change. The BMW 120d is 180bhp 1400kg and 7.2 seconds. thats 128bhp per tonne.
The up at 120 bhp would be about the same power to weight of 128 bhp / tonne assuming a 935kg car, to allow for slightly heavier components