The toilet comes (came?) in 1.6g and 1.28g versions. Performance is about the same. A bunch of the difference is in the refill calibration, the 1.28g version is more precise so less gets dumped down the drain (most toilets overfill the bowl some). Don't know if the prices are different, but if the two are different, when it comes time to replace say the flapper, if you don't use the right one, performance may suffer or you'll end up using more water than it was designed for.