Speaking as a fellow very tall individual flying Icelandair: check back on your seat assignment every week or so and make sure it is still in an extra legroom area. I bought Extra Legroom in June for my September IAD-KEF, but lost it when they changed the flight to a different aircraft type a couple weeks after I booked. I contacted them on Facebook Messenger to ask them to fix it, and they reassigned me to the equivalent seat on the new plane with no problem.