Ok...variation on the OP's original question.

I'm currently booked in F on LH778, FRA>SIN. I'm connecting from SEA>FRA on an LH 330 in F.

My final destination is Bali, and I'm booked on the last flight of the day, at 7pm or so.

If I stick with this itinerary, I'll be in FRA, and thus the FCT, for 12 hours. However, if I take LH to LHR, I can catch SQ319 LHR>SIN, and arrive earlier enough to catch the 4pm flight to Bali.

Who would advise I stick to LH, the FRA FCT and a 12 hour layover, vs the extra hop to LHR, (4 hours in the VS clubhouse) SQ319 to SIN, and then MAYBE catching the 4pm SIN>DPS flight (if I don't, I wait 5 hours in SIN - in the C lounge).

How would weigh this choice?