Purdy is a really nice story as a Mr. Irrelevant this year.  But going up against a top-3 front-7, from the standpoint of QB-pressure, won't be easy.  Dallas has a number of players that can get to him, the passing windows will be much smaller (unlike last week against Seattle - 2nd worst team in the playoffs from QB-pressure perspective), and of coruse the overall pressure of the moment higher.  This is the last game of the week, on a Sunday evening, with a huge audience....unlike last week, first game of the weekend on a Saturday mid-day.  I think we'll see a little bit of a downgrade from Purdy.  And with that, mistakes might happen, the rest of the team will tighten up trying to do too much, and San Fran's execution should suffer.  I expect a close game and expected more of a FG-type of a spread.  Anything above that is value on the dog. 

Good luck