The speech path should present more than a skill check challenge - there needs to be some other obstacle associated with it. I usually veer toward exploring conversations (asking about back history, reading lore, discovering evidence to a criminal case), exploring the environment (discovering an enemy encampment, learning a secret path into a fortress, discovering a rival caravan is already sending an emissary to scout a new trade route), or being able to draw logical connections between two topics... as an example, without it being given as a quest objective, realizing that the local historian who's obsessed with the Montaine family tree would be interested to learn of an exiled Montaine living in a remote city, and then returning to tell the historian that is a simplistic example of paying enough attention to a conversation and its topics and remembering who might be interested in that information... but again, this involves the player remembering and knowing who to speak to next. We sometimes do this within a dialogue tree - if a player has enough presence of mind to return to a previously-asked dialogue node once they've obtained information learned from a later node is an example of a speech-based challenge.
We did something a little different with the Fallout 3 pen-and-paper game and also with Alpha Protocol - in the Fallout PNP game, we allowed players with a high Speech to gain a little mini-dossier psychology profile of the temperament and the psychology of the person they were speaking to either by purchasing them or speaking to them for X period of time - what the NPC's triggers were, what they were uneasy about, what they got angry about, etc, and then once the player had that information, then they would attempt to use those triggers (without the need for a speech check) to manipulate a situation. As an example, when we were playing Boulder in Fallout PNP, Josh Sawyer's character Arcade got a dossier on the leader of the Boulder Dome, enough to realize that the leader would almost always refuse any request or become unreasonably angry if a comment was phrased as a challenge to his authority or any hint that he was managing the situation improperly - but almost any other comment that built up the leader's skill as a manager or drew in a compliment about the progress he made would almost always generate a favorable response, and then Josh could choose how he wanted the target to respond by structuring his comments and debates accordingly. If he wanted to make the leader mad and lose face in front of his followers, he knew how to do it - if he wanted to make the leader agree to a course of action, he knew how to do that, too, but there wasn't a "speech check" to win the conversation, only hints on how to manipulate it. Alpha Protocol did this a bit without a speech skill - if you gathered enough info on an opponent (intel), it began to give you a picture as to what attitudes (aggressive, suave, professional) and mission approach (violent, stealth, diplomatic) they respected and what they didn't, and the player could use that to navigate the conversation to achieve a desired result, even if that result was something that might seem unfavorable at first, like making the person angry.
And you should be able to fail despite your high stats, just like in combat.