I would go through Dulles just to avoid the long layover...and get all those extra miles credited toward GS next year. Domestic F is not the end of the world..you could stay at IAD for 11 hours and catch the 5:30pm flight to SFO on a 777 if you want...but that's way over kill in my opinion unless you had something to do in the area that day.

That said I probably would not take that flight on the 2 class 767... I'd catch the next one about an hour later on a 757. I prefer F on the 757 to the 767..wider seat and slightly more space between you and your seatmate.

Customs at IAD that early in the morning shouldn't be too bad. From posts on here though I do not believe the midfield customs area is open yet so you'd take the people mover over to the main terminal arrivals area, clear customs & immigration, and then go thru security and take the people mover back to the mid field terminal. But you'd have plenty of time to do that.