Hi FlyNFish,
Dreamfoam doesn’t make the memory foam itself … only the mattress.
The density of memory foam is the single most important factor in the durability of the foam regardless of it’s formulation but there is no way to quantify how long any specific mattress or combination of materials will last for a specific person or predict exactly when you will decide to replace it because it is no longer suitable or comfortable for you (because this is the only real measure of durability that counts) because there are too many unknowns and variables involved that are unique to each person. If a mattress is well inside a suitable comfort/support range and isn’t close to the edge of being too soft when it is new and meets the minimum quality/durability specs that are suggested in the guidelines here then it would be reasonable to expect a useful lifetime in the range of 7 - 10 years for more average weight ranges. There is also more detailed information about all the many variables that can affect the durability and useful life of a mattress relative to different people in post #4 here and the posts it links to.
When you are heavier than about the lower 200’s or so then I would tend to reduce or minimize the use of 4 lb memory foam and since you are on the very edge of this range it would probably be reasonable to expect that the useful life of a mattress that contained thicker layers of 4 lb memory foam would be a little less and treat anything more than that as being “bonus time”.
Phoenix