As one who does the BOS-ORD-Asia thing a lot, I always leave as much time for the ORD transit as possible. I usually take the 6am or 7am from BOS-ORD, even if it means hanging out at the RCC or IFCL for a number of hours. I know too many people that have missed the connection for a variety of reasons, including the "through flight" 881; the NRT-bound flight does not hold for its ex-BOS mate!