Speed[]
The Endermen can teleport from any projectiles at very close range. While it wouldn't be direct speed, it would account for reaction time.
The speed of an Arrow in Minecraft is 100 m/s.
While it isn't clear, the Enderman can react from an arrow close enough to almost touch them. Though pixel scaling isn't an option, the smallest unit of measure in-game for horizontal movements is 0.001 of a cube.
As for the time an arrow would take to cross that distance...
0.001/100= 0.00001 of a second. According to our reaction page...This is Massively Hypersonic.
Given that Steve's sword strike can outdo the Enderman's reactions, it would scale to everyone's combat speed.
It would apply to pretty much most characters.