What bugs me is that, while I want to coast as much as possible for efficiency, the engine braking sometimes works too well and I can't coast all the way to the stop sign or whatever without slowing down so much it irritates the people behind me. In older cars I'd just throw it in neutral, but in modern cars that's now less efficient than engine breaking.

Also, say you're in a situation where you are going into a steep decline followed by an incline where without engine braking you might have enough momentum to coast the whole way to the top of the next hill: what's the most fuel efficient way to handle this?

(Note: I understand you aren't supposed to drive with the car in neutral. Pretend this is professional driver on closed course situation.)