Right. The 6'4 guy will be faster because he covers more ground. It's also important to note that speed matters 4x more than acceleration. For example, You have two WRs who are 6'0. One WR is 75 spd and 90 acc and other is 90 spd and 75 acc. After the 1st 10/15 yards they will both accelerate at the same speed and then the
90 spd WR will leave him in the dust after that.
https://www.youtube.com/watch?v=o4px49nscvk