I agree with Sara. stbxH's sex stories didnt matter to me that much. The lies and deceit plus the fact he loved her, did.
Anyway, to your question: I dont think you can decide that now. And ironically I dont think it is even your decision. If Mrs Smiley comes thru and does the walk, then my friend you will have no doubts. Hypothetical questions can torture your head. Stick to what you said before :keep an open mind and watch your wife. If she convinces you she is serious then you pop over to piecing and live happily ever after (ok, exaggerating a bit)
Personally, I believe very few WASs come back to do the work and show committement. I hope your wife turns out to be one of them. K