The most damage you can inflict is 558, provided the victim isn't wearing armour. The P90 at
this range does 99 and then an AWP headshot IN THE FACE does 459. I tested from a number
of angles, as well as above, below and INSIDE HIM and the result was the same. 558.
With armour you have to adopt a different strategy. The AUG from this range inflicts
99 and a point-blank awp ONLY does 448, making the maximum damage 547.
But that's not the most damage that can be done to somebody. If you fall a large distance
you can sustain more. Vertigo will inflict 4999 but that's nothing compared to stepping
on lego, which will inflict upwards of 2 billion. Ouch.