Anyone have any caselaw on how far a person must drive in order to constitute "fleeing"? What is the standard? Caselaw please.

Have a look at Jackson v. S., 718 S.W.2d 724 (Tex. Crim. App. 1986). Distance traveled is not really significant so long the defendant knew that the police were attempting to arrest him, e.g., by using lights and sirens. Let me know if this does not address your concern.

It's like obscenity, you know it when you see it.