Perhaps then, the way out is to find a WP:RS that says that these Christian sources may be inflating the figure. Then the article could quote the higher figure (some Christian sources say that the proportion of Christians may be as high as 15% but according to XXXX these numbers may be inflated). Or, if the source (the one claiming that the christian sources are unreliable) then it would be ok to drop the higher number and relegate the info to the religion sub-article. However, failing an external [WP:RS]] confirmation of the motivations of these 'Christian' sources, it is WP:OR to state that 'it's in the interest of these Christian sources to overstate their numbers'. At best, it is as speculative as 'the Egyptian government allegedly being interested in promoting a lower percentage of Christians because of its troubles with Islamic fundamentalists', which, BTW, I did not say is true or even my view, I presented it as a counter hypothesis to the speculation of biased christian sources. The point is that we can't speculate about motives because we don't do WP:OR. We need to look for external sources to guide us on the veracity of information out there. If we can't show that a source is unreliable, and the source is reasonable, we should present their statistics with the appropriate caveats.  (sniff out my socks)