Very high upgradeable fares
I suppose the upgrade on the transatlantic leg is the most crucial, although it would be nice if I could upgrade the Rome/Thessaloniki leg, too.
The main problem with overseas upgrades with Delta is that the upgradeable fare is SO high, much higher than most airlines charge. You can almost purchase the business class fare outright with not much difference between that and the upgradeable fare. If anyone has any suggestions for getting a business class ticket for under $4,000, let me know!