The numbers of 75% voting for Republicans is better drilled down with number of regular attendees - and to which whatever the religious flavor - increased attendance leads to GOP voting on average
The up to 80% is white evangelicals in general, and regular attendees=even more conservative. The only level of that detail as regards voting that I have is,
Exit polls in 2008 reported that weekly churchgoing Catholics voted for John McCain over Barack Obama, by just 50 percent to 49 percent. Weekly Protestant church attendees voted for McCain over Barack Obama 66 to 32 percent. http://www.catholicnewsagency.com/news/churchgoing_catholics_chose_mccain_over_obama/
In the 2012 election (preliminary exit-poll analysis), white Evangelicals (23% of the electorate) voted 79%/20% Romney/Obama; Protestants overall (53% of the electorate) voted 57%/42%; black Protestants (9% of the electorate) and other Christian voted 5%/95%; Catholics overall (25% of the electorate) voted 48%/50%; white Catholics (18% of the electorate) voted 59%/40%; and Hispanic Catholics (5% of the electorate) voted 21%/75% Romney/Obama http://www.pewforum.org/Politics-and-Elections/How-the-Faithful-Voted-2012-Preliminary-Exit-Poll-Analysis.aspx
Weekly Church attendees (28% of the electorate) voted 57%/39% Romney/Obama; more than weekly (14% of the electorate) voted 63%/36% and “never” attendees (17% of the electorate) were at 34%/62% Romney/Obama. ^