And IMO the impetus on Gingrich in SC is even stronger than it is on Perry. If Gingrich cannot top Santorum and Perry in SC, he should get out, it should be a very friendly state to his candidacy. Whereas if Perry can come in a strong second, he can make the case to stay in.
Whoever comes in third should definitely get out.
Since the delegates are not winner take all (that will change on Super Tuesday - March 6 - I believe) it would be wrong for a solid, consistent conservative to drop out now, (we've seen the roller coaster-musical-chairs nature of this primary) and possibly leave us without a viable candidate.