Hi FlyNFish,
Only you can decide which of them would be a “better buy” because it would be a preference choice more than a “better/worse” choice. For some people that preferred the feel and performance of the latex middle and bottom layer it would be a better buy and for others that either preferred the polyfoam support core or that couldn’t tell enough of a difference between them to justify the higher cost it wouldn’t be.
As I mentioned in my last reply … the main difference would be in how the two mattresses compared in terms of feel and PPP and whether they could feel the difference between the polyfoam and the latex enough to justify the higher cost.
The upper layers are the weakest link in a mattress in terms of durability so there wouldn’t be a great deal of difference between 2.8 lb polyfoam and latex if the top layer is the same.
The top layers and the cover would also have the biggest effect on sleeping temperature and since they would be the same in both the different foam materials in the deeper layers would also make little difference in temperature regulation.
There is more about the many variables that can affect durability and the useful life of a mattress relative to different people in the quality/durability guidelines here and the more detailed information in post #4 here that it links to.
There is also more about the variables that can affect temperature regulation in post #2 here.
Phoenix