How to differentiate web fonts font-face font-weights?
Always option 1. That way it will correctly use bold in cases when the browser doesn't support or can't download the fonts.

EDIT: One more point I've noticed just now: Don't use bold (700) for "semi-bold". Most font creators suggest a font-weight value for each variant. Usually it's 600 for "semi-bold" (and 500 for "medium").