Hi AnointedMatt,
In terms of density and “theoretical” durability the difference would be minor and insignificant but they could have different properties in terms of firmness, temperature sensitivity, response time, and “feel” (see post #9 here and post #8 here).
When you can’t test a topper in person before a purchase then the supplier you are dealing with will be the best source of information about how the memory foam toppers they are selling would compare to other types of memory foam that are available on the market that they are familiar with.
Phoenix