When using the AF search calendar, they'll often show a route with low taxes, but when I click through to the flight options, it disappears.
Also, if you're looking to book DL w/ AF miles, and you're flying to a city that DL doesn't have international service with, you'll find very few options, if any at all. You'll have better luck searching to the international getaway city, and then paying for your own transportation to that city.