Still, go for oxfords. Don't have to be cap toe. Make sure they're not brogue. People probably wouldn't bat an eye at derbys either, but oxfords are best. 'Black suit or tux' really isn't a dress code that allows for any loafers whatsoever. If it HAS to be one of the two pairs you posted, go for the ones with no contrast yellow stitching, as they'll at least draw less negative attention (but likely still some, since they specifically stated a dress code like this).