Believing religion is disastrously antithetical to epistemic rationality. Practicing religion is potentially quite useful from an instrumental rationality standpoint.
Presumably, epistemic rationality only suffers if you believe untrue things.
The whole idea that religion is concerned with belief is quite a western one. Look at some of the eastern religions, and they are more concerned with what you do and how you live - and do not necessarily place an emphasis on faith.
BHTV episode with myself and Adam Frank, author of "The Constant Fire", on whether or not religious experience is compatible with the scientific experience, or worth trying to salvage.