If 10.5 hours is more tolerable, you can do BOS-SEA-NRT-PVG, with the TPAC part in DL's Y+. The 333 has 2-4-2 seating…in my view better than 3-3-3 on the 777. The NRT lounge is DL's best, with quite decent food to supplement or supplant what you get in Y.