Hi rsvoir,
There really isn’t any way to “quantify” these types of questions because each person will have a different set of criteria that is most important to them. These types of things can’t be “measured” except on an individual level but there is a little more information about an “all latex” mattress vs a latex/polyfoam hybrid in post #2 here. For some people a smaller difference can be a significant or even the most significant factor in their choice and for others the same thing is less important. The goal is to make the best possible choice within your budget that has the highest odds of providing you with the best quality of sleep over the years and sometimes smaller differences can be an important part of your choice. For example … how much “value” would a 10% improvement in your sleep quality have over a period of 10 years? This can’t be measured in objective terms or based on a formula.
I think that jefmoody provided the “best” suggestion I would also make which is to talk with each manufacturer you are considering so that your final choice is based on the criteria that are most important to you and based on your own “best judgement”. Once you have eliminated all the worst options and are clear about the pros and cons of each choice then only you can assign a “value” to each of your finalists and decide which of the objective, subjective, and intangible differences between them are most important to you. Because of your higher weight the quality and performance of the layers immediately under the top latex layer could make a difference in terms of durability and performance and the number of layers that can be re-arranged or exchanged for “fine tuning” may also be important to you.
The previous links I provided include my thoughts about more latex vs less and more options vs less as well.
Phoenix