If you want to talk about relativity, it's not true that you need general relativity to handle all types of non-inertial frames, only non-inertial ones where gravity is significant so spacetime is curved (you can define non-inertial frames for accelerating observers in the "flat" spacetime of special relativity, an example would be the system called "Rindler coordinates"). The coordinate speed of light can indeed be something other than c in a non-inertial frame; in fact, since you have total freedom in defining a non-inertial coordinate system any way you want in general relativity (which is why you are free to make "weird" choices like one where the Earth is at rest while the Sun rotates around it), the coordinate speed of a light beam can be anything you want. However, general relativity also includes the notion of "local" inertial frames in the neighborhoods of free-falling observers, because of the "equivalence principle" which says that in the limit as a freefalling observer does experiments in an arbitrarily small patch of spacetime around them, the results of these local experiments should approach perfect agreement with special relativity. So it is still true in general relatiivity that the speed of any light ray as measured in the locally inertial frame of a free-falling observer passing next to the beam would always be c.
A 2011 report of the Pew Forum on Religious and Public Life estimated that members of Presbyterian or Reformed churches make up 7% of the estimated 801 million Protestants globally, or approximately 56 million people.  Though the broadly defined Reformed faith is much larger, as it constitutes Congregationalist (%), most of the United and uniting churches (unions of different denominations) (%) and most likely some of the other Protestant denominations (%). All three are distinct categories from Presbyterian or Reformed (7%) in this report.