We wouldn't use future perfect with "until", because "until" sees the verb as an ongoing process that is suddenly terminated. Instead, we use present perfect with prepositions that imply that the verb reached its natural conclusion BEFORE the other verb started--prepositions like "before" or some uses of "when". We can also use it with adverbs like "already" or ""just.
I will have spoken before she speaks tomorrow. so she won't need to cover the same material I will have covered.
I will have already spoken when she speaks.
I will have just spoken when she speaks.
I know she will arrive late, so I *will speak* until she arrives.