For TATL routes either on 006 or 074 tickets, it is now all fare based mileage and MQD earnings (as long as all flights are either DL/KL operated). It does not matter which is the marketing carrier. Other than Y/B fares, coach fares earn 100% MQM's no matter who markets the flights. This is all covered here --
http://www.delta.com/content/www/en_...-airlines.html
Okay, so as long as JFK-KEF is classified as TATL (which I'd logically think it is, but DL, along with all airlines, can have some strange geographic classifications sometimes), then looks like I should be covered. Thanks.