I was messing around with the dropper block and dispenser block at the same time and I noticed that they both act the same way and fire any item out at the same speed. I thought the dropper block was suppose to drop items not fire them. as you can see in the screen shot they are both being fired out at the same time and at the same velocity and distance.

to recreate just make a wall with a dispenser and dropper block one on each side of the button, lay down some tracks under both the dispenser and the dropper block, and but mine cart with hoppers in them under both the blocks. you will see what I mean by they act the same way.