I'm assuming the OP's concern is with vertical clearance, not horizontal. I'm using the Crud Racer mudguards on my rain bike with 700 x 23 Gatorskins and the fork width doesn't matter; the mudguards don't interfere horizontally.

Vertically the Cruds take up a extremely tiny amount of space. It's amazing how thin they are. It might be worthwhile trying them with the 25mm tires and see if they fit.

I don't know how much reduction in diameter you get by going from a 25mm to a 23mm anyway.