To go back to the OPs question, Saturday is probably the worst day for SFO-FRA, as if you want to be in the office on Monday in Europe, whether going there or returning there, you need to leave Saturday or earlier. the value of lie-flat seat is to address the time zone shift issue and allow people to leave SFO on Saturday, arrive mid-day Sunday and go to work on Monday.

Those going Sunday will, at a minimum, miss part of the Monday workday and have an even more challenging time-zone shift, so do that but many people the local nights sleep that Saturday departure allows in SFO-FRA. Saturday departure for SFO-FRA/MUC was always my choice with driven by work requirements.