It might be worth booking as a DONEx and using CX, BA, AA miles to upgrade to F on flights with a true F cabin. I upgrade DONEx AA flights this way all the time. A few years ago I upgraded a CX DONEx flight using AsiaMiles. Also a few years ago, I tried to upgrade a BA DONEx flight but BA said it wasn't permitted on RTW fares, not sure if that was accurate or if it's still the case.