Paul will go nowhere after Iowa because the Republican Party will not nominate someone who would abandon Israel and ignore Iran. So the real top 4 are Romney, Santorun, Gingrich and Perry.
Romney will take New Hampshire - that's a given. Santorum does not have a strong organization, nor the financing to go much further. So, going into the all-important South Carolina, we'll have Romney, Gingrich and Perry.
Perry has the money. But Gingrich has the popularity in SC, so it's a toss-up right now. But I am predicting that the nomination will be between Romney and either Gingrich or Perry, depending upon which one has the strongest showing in South Carolina.
My bet is on Gingrich, because between now and SC, there will be debates. And Gingrich will clean Perry's clock in those. And he'll probably beat up Romney, too.
I think it will shake out as Romney vs Gingrich, unless a powerhouse Dark Horse like Palin enters. Then all bets are off.