I think primary weight of the first ten states (Iowa, New Hampshire, Col, Minn, Utah, NY, NC, Mich, Nevada, and SC) is what matters...with Iowa and New Hampshire carrying a bump-up each.
Rand Paul can’t win or place second in any of these. Walker ought to win six of these minimum. Cruz might carry two of them. Bush will finish second or third in all ten...meaning that he’s out of the picture by the end of Feb.
Toss in the effect of the debates, and it’s mostly a race between Cruz and Walker, with the other guys carving out thirty-percent of the overall primary vote by the end. No clear winner till the convention.
New Hampshire is crucial for Bush. My guess is he’ll put in a token effort in Iowa and roll the dice on the Granite State. If he doesn’t win there he’s likely done as a serious contender.