The operable word is discernible. I doubt even a lifelong professional fly angler could tell you based on performance what type of guides (single foot or snake) a rod had on it if he/she was blindfolded and everything else (rod size, reel, line weight etc.) was the same.

Given that the amount of metal is actually about the same between both types of guides, the main weight difference is in the extra thread and finish for the second foot. A fraction of an ounce total perhaps for the entire rod?