The Sanagloss does make a difference.
I recommend them to people on wells.
I've sold over a thousand of the Sanagloss Toto toilets.
And have both Sanagloss and non Sanagloss in the home.
The Drake, because the tank is higher, generally gets a higher MaP score,
however in real life, it hardly matters.
The one-piece Ultramax has some advantages in keeping it cleaner, and there is less to go wrong.
But either would be fine.
I think the 1.6 is fine,
With the 1.28, they work, and if you want more water, you can hold the handle down a bit.