Synergistic surfactant blends are disclosed. In one aspect, the blend comprises an anionic surfactant and a metathesis-based cationic surfactant comprising a quaternized derivative. The quaternized derivative is a quaternized fatty amine, quaternized fatty amidoamine, imidazoline quat, or esteramine quat made from a metathesis-derived C10-C17 monounsaturated acid or its ester derivative. Also disclosed are synergistic surfactant blends comprising a cationic surfactant and a metathesis-based anionic surfactant comprising a sulfonated derivative. The sulfonated derivative is a fatty ester sulfonate, fatty acid sulfonate, sulfoestolide, fatty amide sulfonate, sulfonated fatty ester alkoxylate, imidazoline quat sulfonate, sulfonated amidoamine oxide, or sulfonated amidoamine betaine. The synergistic blends have a negative β value or a reduced interfacial tension (IFT) when compared with an expected IFT value calculated from the individual surfactant components. Blends of the invention also exhibit surprisingly favorable solubility profiles. The surfactant blends are useful for laundry detergents, dish detergents, household or industrial cleaners, personal care products, agricultural products, building materials, oil recovery compositions, emulsion polymers, and other practical applications.