I would argue that by staying high as long as possible and then descending with the least fuel flow setting (basically power off glide), you would get the best fuel efficiency. What is interesting though (and something we have discussed in my company) is weather the extra time this will cost you, reduces the savings margin. By going in as fast as possible for a longer period of time, you save time and thus there is less time to burn fuel, although, you will burn a higher percentage at lower levels where fuel economy is poor.
I'm sorry, I can't answer your question based upon facts and spectacular graphs, but I'm inclined to agree with you. I think the reason most of us plan our descent to maintain the highest speed possible is that this minimizes the time in the air. What is more expensive than fuel is maintenance costs and by getting in as many legs per flown hour between overhauls you optimize the aircraft's production.
/LnS