I use syn. gut in my racquets and while thinner 17 ga. options seem to have better feel at higher tensions compared with thicker string that can feel clunky, I haven't seen too much difference in actual performance. My frames are soft 'n cozy Volkl C10's, which have worked fine for me with both gauges of string. Since their feel is completely acceptable with the fatter strings, I use 16 ga. for the better durability and haven't had any sense of losing out on spin potential, etc.
I also string for a few serious sluggers who like to play with hybrid setups and the only reel of poly that I stock right now is 17 ga. Since it's so much tougher that the softer crosses, I haven't had the need for a thicker poly yet. Usually when someone is looking for some better feel in general, I think that a thinner gauge can be an easy solution, especially in a racquet with a dense (18 mains) pattern.