Hi jim8,
As you probably know … Select Foam is a member of this site (which is by invitation) which means that I consider them to be among the best quality/value manufacturers or outlets in the country. Of course it’s also a nice perk that the manufacturing members also provide a bonus or 5% discount on a mattress purchase if you mention your membership in the forum 
NOTE ADDED: Select foam used to be a member of this site but because of ongoing customer service issues and delays their membership was terminated and I would read the warning here before considering them.
There are many online outlets that claim their mattresses “match up” with the Tempurpedic line in either quality or value but in most cases this is only marketing and the quality or materials or the layering or construction of the mattress is more of an apples to oranges comparison. It is often used by “cheap” memory foam manufacturers or outlets to try to convince consumers that “all memory foam mattresses” are the same and that lower density cheap memory foam is just as good quality as higher quality versions. Of course this isn’t true at all.
In the case of Select Foam though … they really do use equivalent or better quality materials and they use their own personal testing and that of customers in their bricks and mortar outlet (where they have their own and the Tempurpedic line set up side by side) to legitimately “match” their models to the Tempurpedic line. This is part of their “value” and part of the reasons I invited them to become members here (see the welcome message post #12 here)
So yes … this would be very close to an “apples to apples” comparison in terms of quality and performance as much as is possible between any two different mattresses.
Keetsa as you mention is a Chinese manufactured mattress (made by Zinus) which uses lower quality foams and materials and has a somewhat overblown focus on being “green” when in fact polyfoam and memory foam is anything but green. I would not put them in the highest value range although they are better value than some other larger manufacturers but you would need to know the specifics of the materials in the mattress you were considering and compare them to others that used similar lower density/quality materials for a real apples to apples comparison.
Dixie foam is also not an “apples to apples” comparison but for a different reason because while they use high quality materials in their mattresses … they don’t make mattresses that are designed to “duplicate” the Tempurpedic line but meant to provide a different series of choices to meet the individual needs and preferences of their customers. While some of their mattresses may “match” a certain Tempurpedic model in the perceptions of some people (different people will often perceive the same mattress differently and different mattresses the same depending on their body types, sleeping styles, and preferences and sensitivities), this would be by co-incidence and not by design. They are one of my favorite manufacturers in the NYC area and their mattresses are also high quality and among the best value.
The only thing I would caution you about is the use of such thick layers of memory foam which can be a more “risky” material than fast response foams although this “risk” is lowered somewhat by the use of higher density memory foam. This is because memory foam changes in feel and performance over the course of the night according to temperature, humidity, and time spent on the mattress so when you are considering a mattress that uses this amount of memory foam, it’s especially important to make sure that no matter what the quality or value of the mattress materials, that it matches your needs and preferences as much as possible when it warms up and that you test it objectively for PPP (Pressure relief, Posture and alignment in all your sleeping positions, and Personal preferences). Many of these “preferences” are listed in post #46 here.
I normally recommend spending at least 15 minutes on any mattress that you are seriously considering to make sure that you test as objectively as possible for PPP completely relaxed and in all your sleeping positions but in the case of memory foam … especially with layers this thick … I would recommend at least double this to make sure that you are also testing for the performance of the mattress after the memory foam softens with your body heat.
Hope this helps.
Phoenix