how about Icelandair? approx $2200, approx 90-min connections each way ... I'd have to suppose KEF is a relatively easy airport for transfers ...

I misunderstood that. I thought that they were comparing the two connecting flights to the one in FRA. I must have been reading too fast.

Even so, I'm sure they're not going to want to take a train, as they'd have to deal with their luggage. I would think an airport transfer would be far easier in that regards.

I was thinking about Icelandair, too, but jer wants to fly the longer leg in a wide-body aircraft, and Icelandair uses 757s. The other issue, regarding sleep, might be that neither leg is particularly long when stopping in KEF.

For probably the lowest fare and also the longest uninterrupted flying time, there would be Aeroflot via SVO. This sounds horrible to me but I know people who would choose it.

agreed that the 757 isn't an ideal FC/BC aircraft, and KEF isn't a particularly long haul from either the east coast of the US or AMS

someone upthread suggested TK via IST, which is actually 400-some miles farther (approx .75 hour longer) from IAD, and runs ~$3300 ... unfortunately the outbound schedule has a night arrival into AMS (or an overnight in IST), and the return involves a short redeye from AMS (or another overnight)

I very much concur with you in this regard. It sounds like they want the easiest, most pain-free transfer they can find. Transferring to a train does not meet that condition.