Hi knlmwq,
Out of the three choices you are mentioning two of them are 4 lbs and the third is 3.2 lbs so I would first eliminate the 3.2 lb memory foam because it is lower quality/durability.
The overstock toppers also don’t mention the type of gel memory foam that they use. “Infused” could mean an infusion of either particles, beads, or liquid gel. Large gel particles that come out of the foam easily are less durable and can break down the foam faster … smaller particles that are embedded into the cell walls of the foam rather than the cells of the foam won’t degrade the foam to the same degree as larger particles. Gel memory foams that use particles will also often use a higher percentages of gel in the foam which has its own benefits in terms of support and cooling.
Unfortunately … the foam manufacturers don’t provide enough specifics of the gel they infuse in the memory foam (either particles or a liquid polymer) so you are really dependent on the knowledge, experience, and integrity of the retailer or manufacturer you are dealing with to make meaningful comparisons between them. In practical terms … I would treat the density of a gel memory foam as being a close equivalent to a similar density in a regular memory foam in terms of durability. I would also keep in mind that different types of gel memory foam also have different properties (depending on the technical details of how it is made) which can lead to a very different feel and performance between gel memory foams of the same density. Post #2 here has more information and links to other posts that may be helpful in making your choices.
Once you are down to roughly equivalent quality (defined in terms of density and durability) … then your personal testing and experience on each topper would become the most meaningful difference between them (assuming they both meet the memory foam guidelines in post #10 here). Since they are both online choices that you can’t test ahead of time … then the knowledge and experience of the retailer or manufacturer you are dealing with and their ability to provide you with information that is accurate and meaningful to you about their toppers and how they may differ from other toppers available and any return policy they may have would become the most important part of the “value” of a topper purchase. This would be a much more important part of deciding between two choices than trying to analyze technical details which may not be available anyway and would require a degree in foam chemistry to fully understand.
In the earlier days of gel memory foams when most of the particulates were larger this may have been correct but as the gel memory foam technology has developed and second and third generation gel memory foams have been released then in most cases it is no longer as meaningful a comparison. Each of them would have their own strengths and weaknesses. Gel memory foams themselves are also not necessarily cooler than “regular” memory foam that is more highly breathable. Unless you are looking at gel memory foams that have much higher percentages of gel (in the range of 25% - 30%) then the cooling benefit of gel would be temporary and the main benefit of the gel would be its ability to improve the support characteristics of the memory foam (again depending on the gel type and content) more than the ability to keep it cooler.
The price difference between the two 4 lb choices you have is small and not particularly meaningful and I would base your decision on the other parts of “value” besides price including your conversations and the information you receive from each of them, your confidence that the topper will be suitable for your needs and preferences, and any return or exchange options you have after a purchase.
I would also keep in mind that there are many elements that affect temperature regulation in a mattress besides just the foam (see post #2 here) which can be just as important as the foam itself.
Phoenix