Perry can be a strong and motivating voice in the course of the election without sucking votes away from the other two conservatives (by remaining in it).
His influence doesn't hinge upon his presence in the race. What does hinge upon his presence in the race, are real, countable votes. With the polling margin as thin as it is going into SC, it's hair-raising to think that the few votes Perry takes from Gingrich might put Romney across the line for the win.
Get out now, Perry, and use whatever pull you have with your supporters to help put Newt ahead of Romney.
Also, people need to be realistic about Santorum. He cannot win the general election and people need to face that. He can go out now, or after SC and endorse Newt. Regardless, he will be out later. If Santorum stays in to take votes away from Newt, he may end up with some scrap of an appointment from Romney, but Santorum supporters will be putting in a person who has the opposite social views as they have, Romney or Obama. Santorum voters need to bail on him now. They are holding out for their perfect social candidate and will end up getting the worst. I can understand why people support him, but don't understand how they believe he can win. Romney has been chosen and the only one they are afraid of is Newt. I also think they know if they throw something Paul's way he will swing his voters to Romney. Paul has pretty much said that. Santoum vs Romney/Paul voters, NO WAY. Heck, even Newt won't be able to do that unless Santorum backs Newt.