You may not be aware but fares to/from LHR are not the most cost effective MR's. My trip YOW-LHR in April costs 11 CPM, as compared to as little as 5.5 CPM for destinations in Asia-Pacific.

For your future reference, I find a useful tool for fares & CPM's is:

http://www.farecompare.com/search/flyertalk.html

For now, it sounds like you have already decided on SFO, and are looking for validation that its a good MR (it is not).

ps PM me for that beer next year!