I have done a mini experiment. I have determined the speed at which a player can throw an enderpearl. To do this, I dug a 2 block deep hole, placed a stone slab at the bottom, and crouched, to get my eye height as close to ground level as possible. Next, I threw the enderpearl straight into the air. I did frame analysis, and discovered that it took 2.2 seconds to reach peak height. I then used this equation:
vf = vo + a * t
Substituting the known values, I got:
0 = vo + -14.4622 * 2.2
0 = vo - 31.81684
vo = 31.81684 m/s
This means that a player throws an enderpearl at a speed of 31.81684 m/s.