Hi amyhunter0204,
There are too many unknowns, variables, and personal preferences involved for me to know which mattress may be the best match for you in terms of PPP. The only effective ways to choose a mattress is either with your own careful and objective testing or sleeping experience or with a more detailed conversation with a knowledgeable and experienced manufacturer or retailer that has your best interests in mind and that can use the information you provide them to help you choose which of the options they have available would have the best chance of being a good match for you based on “averages” (see mattress firmness/comfort levels in post #2 here). If both of the mattresses you are considering use 100% natural Dunlop or Talalay then I would certainly consider both of them to be good quality and durable materials although if the Dunlop in the lower cost option is mostly synthetic molded Dunlop I would put 100% natural Dunlop in a higher quality and more durable (and more costly) range.
ILD in latex is measured on a 6" core (not 4" like polyfoam) and if the ILD is measured to a 25% compression it would be the amount of force needed to compress a 6" core down to 4.5". No matter which type of latex is being tested … if they are the same ILD then the amount of force used to compress it by 1.5" would be the same no matter which type of latex it was. Different types of latex have different response curves though so if you compress different types of latex that are the same ILD either more or less than 25% then the amount of force required would be different from each other and they would only “match” at that specific percentage of compression. There is more about ILD and compression modulus (both of which are part of determining the softness of a foam material) in post #6 here.
Post #6 here also has more information about the different types and blends of latex and I would treat 100% natural Dunlop and blended Talalay as “equal but different” and both are very durable materials. I’m not sure what size mattress you are looking at but if you are looking at a 6" Dunlop core with 2 or 3" of blended Talalay latex for only $700 then I would suspect that the Dunlop may be mostly synthetic molded Dunlop in which case it would likely be less durable than 100% natural Dunlop and would have a greater chance of developing impressions over time than 100% natural Dunlop.
Phoenix