I've been reading this thread, and had a question on the following itinerary:

SFO to LHR (stopover)
FCO to NRT (destination - OJ used)
NRT to SFO

The above is my intended US to Asia roundtrip with a Europe stopover, which would use up 120k UA miles in business class. However, on the final leg (NRT to SFO), do I need to return via Europe, or can I cross the Pacific? I've been a little confused since some seem to report success, while others have mentioned that trans atlantic and trans pacific in a single itinerary constitutes a RTW. Thanks.