Hi yukoncornelius,
Latex and memory foam are very different materials… They’re sometimes described as being at opposite sides of a spectrum. The value they have, and specific layering/thickness, are only relevant to the extent they accomplish suitable PPP for you. (I’m assuming you’ve checked out the first post, here,https://forum.mattressunderground.com/t/how-to-look-for-and-find-the-best-mattress-for-you-read-first). That is to say, a mattress has no value to you if it doesn’t match you, regardless of the thickness or materials use - it’s a bit like clothing, if a pair of pants don’t fit it’s largely irrelevant if they are the most trendy, luxurious, or well made pants, they still don’t fit).
Also note, just because the materials on paper look good, doesn’t necessarily mean you will like the feel of a mattress. There are all sorts of things they do with mattresses, and as Phoenix says every layer will interact with every other layer. You need only check termpurpedic and the fleet of vendors making replica mattresses to see there is a wide variety of feels they are going for, which is more than just a measure the thickness and the densities. It’s where the science becomes art 
Anyhow, the short answer is… If you’ve tried and like latex in an identical configuration, then those deals on 8" latex may be wonderful for you. There are lots of people who prefer memory foam (and they feel and behave totally different), or a different configuration of latex. To those people, such a ‘deal’ is relatively meaningless.