what does "Fast is my best speed."mean?
He opened the passenger door. “Remember, once we get to Maureen’s we need to move fast. We don’t know how long he might wait.”
“Fast is my best speed.”
When they pulled up at Maureen’s, Eli grabbed the bag holding his change of clothes, Abra’s shoes.

Question

what does "Fast is my best speed."mean?
He opened the passenger door. “Remember, once we get to Maureen’s we need to move fast. We don’t know how long he might wait.” 
“Fast is my best speed.” 
When they pulled up at Maureen’s, Eli grabbed the bag holding his change of clothes, Abra’s shoes.

Answer

He's saying he's fast, and that he'll be in and out of Maureen's house quickly. Kind of like "be fast." "I'm always fast."

Answer

There is no secret meaning here. The person states that going fast (rather than medium or slow) is the best speed for him or her.