Personally I would consider 0-60 in 4.4 seconds as being fast. 155mph electrically limited top speed is pretty standard fare for BMW. At the end of the day the I8 is a massive car, honestly, its yuge. The I8 isn't designed to be a hardcore track car. Even in sport mode the suspension is still pretty soft, the ride quality is genuinely impressive. Its not designed for the track. Its designed for daily driving and efficiency, for a car that does 0-60 in under 5 seconds the fact it it gets close to 60mpg(imperial) under spirited real world driving is impressive. I can only conclude that the car doesn't know what it wants to be. The car feels as though it has been designed for the only people who can afford one, frail 60 year olds, however they would struggle to get in and out. Its an excellent grand touring car, if you ignore how small the boot is. But at the end of the day it is fast in a straight line and very cool imo.