Of course 500 Km is a big difference with 400 meters but to those near the point of impact it wouldn't matter and the global effects would still be beyond anything in our history.
This is one interpretation of what this could look like:
The difference between the 500km asteroid impact in the video, and a 400m asteroid impact is the difference between a man jumping, and a man jumping to the moon.
Yes, it is the difference between a sterilization level event and one that is probably survivable. But it would still be the most significant impact in all of recorded history and to get to a larger one you'd have to go back a long, long time.
Yes, it would be survivable for humanity. But depending on where it would happen, how dense the impactor is and at what speed it is traveling the effects would nevertheless be quite serious. Imagine NYC or SF taken out like this (of course the chances of that happening are really small given their area relative to the total of the planetary surface):