I'd never use anything other than museum grade archival boards for mounting clients photo's or any artwork that is to be preserved. The pure cotton rag, non bleached, and chemically stable board will make your art more permanent in the long run. Why chance it? For digital images / prints it might be different, but still no one truly knows how these materials will perform after a number of years. Sure the tests might indicate that they may last, but it's not guaranteed. Silver and Platinum prints have be shown to be archivally stable if processed as such and kept on, or in archivally safe materials. The test of time and countless environmental effects are already known. Do we know for 100% certain that digital and so called carbon pigment inks won't have environmental effects impacting them over time? We don't. Environmental effects alone will cause a regular non acid free board to yellow in no time. Why risk it?