Rich Eisen & his combine "talking head" buddy had a video of 2 players running side by side with only minimal difference is 40 times & it resulted in about 3 feet of separation.
Here’s an example of what the difference of 4.47 (James Pearce) to 4.49 (AJ Brown) looks like (2 hundredths of a second).
Technically a 4.71 to 4.69 would be even closer than this example as the slower the time the less ground is covered each hundredth of a second making the gap even smaller.
Really puts in perspective how meaningless that little difference is. Especially at TE. How often are we sending a TE on a deep 40 yard route downfield. Fannin ran a 1.56 10 yard split which is very good for a TE. Happens to be the same 10 yard split that James Pearce ran.
For a TE that 10 yard time is way more important. He clearly had a good initial burst of speed. He also was good in his 3 cone drill which highlights his ability to change direction and quickly accelerate. These things are far more important for a TE than being able to run fast 40 yards down the field given the type of routes they generally would run in the NFL.
Here’s some examples of Fannin’s quick change of direction and acceleration to create separation during Senior Bowl reps: