I have only flown Y in the 3-4-3 configuration on shorter flights, LAX-DEN and DEN-IAH (both "island" configuration 777-200s with the old business class cabins reused as first class seating). It's the shoulder space that really suffers. Once I had a middle empty next to me, the second time the adjacent passenger was very petite. I would dread facing something like SFO-HKG (on the 777-300, also 3-4-3) in this configuration.