Excellent find, op!
I'm thinking that out of the three US connections, ORD, JFK, and IAD, I would pick IAD.
ORD has the issue with the train that connects terminals down until late 2019 - the bus replacements are problematic - and the AF/KL lounge in Terminal 5 is really mediocre. Terminal 7 @
JFK...ugh! I can't comment on the BA lounge, though. Maybe it's nice. I guess you could go over to T8 for the Flagship Lounge but security @T7 is the worst. IAD uses the great Turkish Lounge and is interconnected so you don't need to go through security again.