Ii have grown the Sapelo Sweet, which is one of yellow granex approved for growing as a Vidalia onion. https://garden.org/plants/view/151836/Onion-Allium-cepa-Sapelo-Sweet/ I don't notice difference in flavor among the Vidalia approved varieties that I have grown. Major differences are maturity dates. Most of these varieties are only available to commercial growers. I have to find a vendor who sells 1000 seed packages. Siegers sells them but I can't use the numbers.

Thank you farmerdill. (I was HOPING you would respond!) Now that I'm looking more closely, I'm more puzzled about brix. Not to confuse onion brix with "sweetness", but at least one reference has a list of sweet onion brixes that range from 6-10, while other sources say that onion brixes are all pretty much the same. So I'm confused. Your finding that Vidalias all taste pretty similar is consistent with the latter.

Re sources, I did stumble upon Twilley Seeds, which seems to sell 1000 seed packages of these. I've never ordered from them, but they seem to get good reviews.

Twilley and New England seed are my go to venders.