The only "bounce" Newt is going to get is the dead cat/bad check bounce. He's fighting with Ron Paul now, nobody else.
As soon as Santorum dropped out, it was Romney's race. Although I will agree we need a preferably Southern rock-ribbed conservative, and while Rubio says he's not interested, he'd fit the bill and then some. Bob McDonnell would be another good choice, Rob Portman is another possibility although he's not from the South (but Ohio is still critical.)
I don't see Romney going with Christie for a couple of reasons--too regional (NJ vs. MA) and people might tire quickly of his bludgeoning style, although they do get along well.