Hi heythisisdave,
When you are dealing with two options that are both in the “best value” range then choices become a matter of smaller objective, subjective, and intangible differences that may be more or less important to you. You can see some of the different factors I would take into account in your own “value equation” post #46 here.
As you mentioned there is always a “risk” in overthinking things (and a risk in underthinking them as well :)). Mark at Dixiefoam does do layer changeouts and as you know I think highly of the mattresses and the quality, value and service he offers. He would certainly be welcome as a member here.
I personally place a lot of value in being able to test a mattress locally for its suitability in terms of PPP (Pressure relief, Posture and alignment, and Personal preferences) and a rough guideline I tend to suggest is that if a local purchase that you have tested is in the range of 20% or so more than an “apples to apples” comparison available online then I would consider them to be “equivalent” value and probably go with the local purchase. When the local premium is more than this, then I would more seriously consider an online alternative. Of course each person can set their own “number” based on their risk tolerance and on what is most important to them so this is just a general guideline.
My goal is usually to help people get to the place where all their choices are good ones and then get out of the way of their final decisions which are more about personal preferences and intangibles but I would take some comfort in the fact that you have eliminated your worst choices and you are in a position that you really can’t make a bad choice in terms of quality and value. All of your choices are better than what I would guess 80% or more of mattress shoppers end up buying.
Phoenix