The inventor of the MAP test says anything over 500 is fine. Many of the toilet manufacturers have figured out how to maximize their performance on those tests. Keeping in mind that what they flush is plastic wrapped waste sausages, nice and smooth, no rough edges, the test isn't of the real thing.
Given any Kohler verses a Toto, I'd take a Toto. Partly because their QA/QC is better, and second, because Kohler tends to use non-standard parts that are not that easy to find. I do not know the specifics of the Kohler model you're considering...some of them do use more easily found parts, and they will need things like seals and maybe a fill valve over their lifetime.
The thing I'd do, is take a very close look at the side of the toilet and look at the path of the trapway - especially at the end where it turns down to the toilet flange and out. On many of their toilets, it tries to make a tortuous tight turn right there...works fine with plastic wrapped sausages, but throw in some 'real' stuff along with paper, and the end result may not be as good. Toto's path is much more smooth and gradual with no sharp turns to slow things or trap stuff, so things just go down well. The prices on anything like this can vary considerably from one vendor to another, so shop around...you can often save a very big percentage off list. Throw in probably the tightest QA/QC in the industry, and, at least in my mind, Toto wins. I have two, and put two in my mother's house.