Do you have an ironic comment on your bike, at least a little carbon something?
I use a BBB carbon fibre bottle cage on a bike that weighs at least 50 pounds in day trim, ready to go paint, or drink tea in a distant estuary with pedal pals. You can't see too much of it because I made an adaptor for it from old braces (the red elastic) to hold in all sizes of water bottles and thermos flasks, for which it wasn't designed.
It's held onto the seatpost, or more precisely stayed off the seatpost and the rest of my bike's expensive custom coachwork, by a really clever SKS adaptor, which is a quick release item (if you know how, otherwise thief proof) though I leave it permanently on the bike as all the other mounting places for waterbottles are in use for other devices.
