Do you mean that social conservatives make up 90% of GOP? I don't have any idea, myself. Is this your best guess or hyperbole?
A third party makes good sense from an ideological point of view. But, from the view of pragmatic politics, it would be close to impossible to create one which is strong enough to win the 2008 general election. I guess it would be perceived from the outside as the right-wing equivalent of Move_on.org. (A group that told the dems: 'We bought you, we own you.')
Hey, it might work...we could call it Right_on.org.
hyperbole
I have seen statistics from 40% to 65%. Although supposedly people who are one issue abortion voters are around 10% of the total.