Hi Mattt,
I personally wouldn’t make the same generalization and it would depend entirely on which area of the country you live in and on the specific mattresses you are considering or are available to you. In some cases online may be worth the additional risk for some people and in some cases local value may be better. It would also depend a lot on your own personal value equation.
Regardless of which may be the case for you … I would always start off with local research and testing.
The Tempurpedic line can be useful for testing purposes because many manufacturers make mattresses that they make fairly specific comparisons in terms of similarity of feel or design or quality of materials (or in some cases all three) to the Tempurpedic lineup so your testing can provide a useful reference point. The Sealy Optimum is not popular enough for most manufacturers to use as a comparison so the value of testing these would be much more limited except as a way to make some very generic comparisons between memory foam and other materials or unless an online manufacturer has specific knowledge of how their mattresses compare to the Sealy Optimum lineup which would be much less common.
You can see more information about the Optimum lineup in post #48 here but they use memory foam in the 4 lb range (in the midrange of quality) and aren’t particularly good quality/value. In most cases the time you spend testing these is only useful if you intend to buy that specific mattress which I wouldn’t suggest.
It would certainly be worthwhile talking with Brooklyn Bedding or any of the other online memory foam manufacturers that are included in the list of better online memory foam manufacturers who in most cases can help you compare their mattresses to the Tempurpedic lineup in terms of “feel”, design, or quality (or all three in some cases) and in many cases use either gel memory foam (of similar or higher quality than the Optimum lineup) or more breathable “regular” memory foam which can also sleep cooler than memory foam that is less breathable.
Phoenix