I would go for AMS-LHR-SFO.

My strategy is always take the widebody as far as you can, I would definitely not consider IAD and probably not ORD if I'm ending in SFO.

LHR seems to have more NC availability than FRA in my experience. The 777 will have the old C, which probably means less paid C and an easier upgrade.

The new C is great, but with two passengers, I'd rather have the better upgrade chance.