Okay, so I've been turning this over in my head all day, and I've come to a rather cynical conclusion.
I was originally thinking of this in terms of Sir Martin being a SK vs. there being a fourth Other, but now I'm thinking in terms of someone being bit. First off, if someone's bit, a reread isn't going to help with that, since they would have been bit last night.
IF there are no more others, there are two possibilities: Sir Martin is an SK, or there is a Walker/player who will become a Walker. Both of these things could actually be true, but that's unimportant to my conclusion.
If the Amph, WW and I lynch Sir Martin and there's no Walkers, then we all win as Group members. If we lynch him and there is a Walker, we would all (presumably) become Walkers eventually, and still win, just as Walkers. So unless we think there's another Other, lynching Sir Martin would guarantee the three of us victory.
The flip side of this is, if we lynch anyone other than Sir Martin today, then Walkers are guaranteed to lose; he's biteproof (I don't know why he would lie about that) and there won't be the numbers to lynch him after today, so he'll just kill any Walkers with impunity. The best hope for a Group member in that scenaior would to be to hope that Sir Martin was telling the truth about becoming a Group member and to make sure that they died before they converted. Luckily for me, I still have my sacrifice ability: if we do end up lynching WW or Amph, I can make myself the lynch and make sure I die as a member of the Group. If Sir Martin is telling the truth, I'll be assured victory; if he isn't, then I'll have lost anyway because we didn't lynch him.
So unless someone can convince me that either WW or Amph is an Other (and I'll be doing my own reread to this end) then basically the only lynch options today are Sir Martin and me. And I still think that "Sir Martin is a SK" is the most plausible scenario, so I'll keep my vote there for now.