I am not really sure, but all I can say is that one year after installing our American Standard 2889.216.020, I LOVE it!!! I find myself comparing it to all others I use in other households and I couldn't be happier than I am with this model. I almost never use the larger flush either as it works so well with the least amount of water.
Is the power of this toilet limited to things on my end? Such as my current piping and water pressure? Or is everything basically on the toilets end? If you don't understand this question I'll try to word it better?