There's no separate First Class line at the International Terminal at SFO. On the other hand, I've never taken more than 5 minutes to clear the screen on either the A side (where VX operates) or the G side, even at international rush hour. There's also a Clear lane on both sides.

If you leave SFO on VX before 10 am, be aware that the VS Club isn't open until then, and there's no alternate lounge.