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In the vast majority of scenarios an hour at SFO or DFW or SEA will be enough time to make the connection. The question is what you'll do if you miss. There's a midnight flight on Asiana from SFO to ICN as a backup option 12 hours late. There are also Asiana flights from JFK or ORD that you could switch to if your BOS departure is running late enough that you know you're in trouble before you get off the ground. The AC flight via YZ is probably the best balance of connection time risk and flight schedule. Plus more time on the long-haul biz product for a more comfortable trip. Where does that price?