i definitely wouldn't pay for 64B which feels like it is basically in the galley. i would much prefer a window seat on the main deck.
my experience from YVR has always been that even though the seat map shows full, when i check in at exactly T-24 (exactly meaning i'm sitting with the cursor on the check-in button as the seconds tick down) I can get a good seat. very often 62A/K believe it or not.
of course, YMMV from SFO.