I’ve only grown nects in the 20’s brix range on a Honey Royale tree that was a terrible producer here. Only one season did wildlife allow me to eat any of the tiny crops and at about 25 brix the fruit was unlike a nectarine to me and more like some tropical concoction- syrupy rather than juicy. No discernible acid, but when fruit gets over about 16 brix, I can live with that.
Here, a good nect starts at about 15 brix and rarely gets more than a few points over that. Once they get up to about 17 I would not find any increase especially pleasing. Commercial ones that get shipped here rarely get higher than 13, which is frustrating given that they are grown in CA where the sky is the limit. I did get a single small flat of very sweet ones from Cosco this year. The little crate touted them as being truly tree ripened (including suggesting the white freckles were the result of high sugar).
Unfortunately, commercial CA growers have largely converted to low acid varieties and never identify their products as such.
American consumers are really ignorant about fruit, unfortunately, so high quality is generally not a huge asset to the seller, nor is any description of the relative acidity of the product.
I got a chance to see what was available to consumers this year because my own stone fruit crop failed due to late hard frost.