Odd post, evidently you aren't aware of who the frontrunners are, and who has the money, organization, name ID, and political staff lined up, along with endorsements and commitments.
As far as rinos and voting, they are more likely to support the GOP than not, whereas the conservative base has reached it's limits, and will give a weak turn out to a Mitt Romney, or a Romney clone, and many tea partiers may go third party and give you the GOP 30% that you think is possible.
You might be right about RINOs supporting a GOP candidate no matter what, but I have to believe that RINOs like Merkowski will force a third party Ross Perot-like candidate into the mix. That let slick willy get elected with 40% of the vote (I think). Sarah will always have my money/support/votes, but I just am not convinced that the left’s relentless character assasination won’t take its toll.