Given it's a party-sponsored gathering, Newt is likely to be at a disadvantage. Santorum's task, for Romney and the party, is to take down Newt so Romney can finally win in the South.
Newt's task is to be cheerful.
I have no worries about Newt outshining Santorum... but there were 2000 seats that were free to the public, supposedly, and I don’t know much they were manipulated. It is also in a theater, so the audience could be a factor.