First, you have to understand that the difference is more important in AmE than in BrE. It is my understanding that "further" is more commonly used in any cases in BrE. Second, there is considerable overlap, even in AmE.
1. I would use "farther" in both sentences.
2. I would use either.
3. I would use "farther".
4. I would use "more".
B is not correct. I would change "than" to "from". A is OK. For C, I would write "than I" or "than I ran".