Hi shift_47_
I can add a few comments to dn’s helpful comments as well …
I’m assuming that the ILD’s you’ve been quoted are accurate because the differential in the zones is more than you would usually find.
I’m also assuming that the covers of both mattresses are the same because the cover and quilting will also have a significant effect on the feel and performance of a mattress.
You can see a few thoughts about covered layers vs uncovered layers in post #2 here.
You can also read more about individual layers vs glued layers (or single layers) in post #2 here and like dn, with a mattress that has a zip cover I would consider individual layers to be an advantage because of the ability to exchange them with a layer that is a different firmness level if that becomes necessary or to be able to replace them without having to replace the entire mattress.
If you have individual “pieces” in the top layer I would also make sure that you have a quilted cover so that you won’t feel the split between the individual pieces or zones (or have tested them to make sure you don’t).
Phoenix