In my opinion "a belief held with absolute conviction despite superior evidence" describes religious belief. Therefore, religious belief = delusion.
Perhaps there is no evidence that God DOES exist, but neither is there any evidence that He does not. So belief in God does not seem to qualify as delusion. Lack of evidence in favor of something is not the same as the presence of evidence against that thing...
For example, belief that the Patriots won the Super Bowl IS a delusion, because there is of course irrefutable proof that they lost. Not the same thing here. There is no absolute proof that God does not exist. So belief in Him may be based on faith, but it's not flying in the face of any 'superior evidence'.
MadBaggins, I once dated a Christian girl. It was fine, until I wanted to have sex, and she wanted to have sex but her religiosity wouldn't let her have sex ("sometimes I wish God didn't exist so we could have sex.").
Which is sad, really, because that's a prohibition that does not exist. Nowhere in the Bible does it ever say that sex outside of marriage is, or even should be, forbidden. (There are warnings against 'sexual immorality' but I interpret that to mean just, well, don't cheat, don't trick people, that type of thing.) It's strictly a personal choice to make.