To be honest there could potentially be nothign between the two engines performance wise.
You could have one 163bhp with a healthy 170bhp and a 177 example with an unhealthy 172 etc lol.
(when i say unhealthy, i dont mean a ill engine or turbo i just mean a car not putting out as much HP as the next, every engine is different due to manufacturing tolerances and how there were run in)
.... But I now have a M3 CS