Hi Jimbo770,
Don’t worry … there are no “quotas” here and if you are wondering or have certain questions then others will as well 
There are different types of alignment which are all important to make sure that the spine and joints are all inside their neutral range of flex when you are completely relaxed in all your sleeping positions (so the mattress is doing the work of keeping you in alignment rather than any tension in your muscles, tendons, or ligaments). This includes horizontal alignment (top to bottom) and rotational alignment (twisting) which can both be a cause of the pain or discomfort that goes with alignment issues. Post #6 here can help you “visualize” the goal of good alignment.
In some cases alignment issues can develop gradually and it can take time to experience symptoms (like other types of symptoms that develop gradually from repetitive experiences or movements) so I would make sure that you sleep on each combination for a few days because a single nights experience can be an anomaly. For example if the spine is decompressed then the discs will be able to rehydrate over the course of the night and maintain their flexibility but if they aren’t then it may take time to develop symptoms that come from the lack of flexibility. Twisting forces are usually worse than bending forces (most people can think of times when even some seemingly innocent twisting caused a back issue). There are three links in step 4 of the tutorial post that have more information about using a combination of visual and experiential cues to test for good alignment but in general terms if there is no obvious sagging when you check alignment visually (which can be a tip off for alignment issues that you don’t notice right away but may develop over the course of weeks or months) and your actual sleeping experience doesn’t produce any stiffness, discomfort, or back pain in the morning then the odds are good that your alignment is probably inside the range of flex that is fine for you.
There is more in post #4 here about all the variables that can affect the useful life of a mattress and influence when you cross the “fuzzy line” when you begin to experience some vague symptoms and begin to tolerate a mattress a little more and sleep well on it a little less. Like aging this is a gradual process that creeps up on everyone gradually over time. Because of this … there is no way to attach a number to this type of question because it will depend on so many variables including your own sensitivity to alignment issues and how close you are to the line between the range of “neutral alignment” that is suitable for you and being “out of alignment” (see post #2 here).
The only thing you can say with certainty is based on a comparison relative to something else and that more durable materials will maintain their properties and last longer than less durable materials, firmer layers will generally last longer than softer layers, deeper layers will generally last longer than layers that are closer to the sleeping surface, and that when it comes time to replace a mattress it will usually be because of the gradual loss of comfort and support over time that begins to produce symptoms rather than because the materials inside the mattress have completely “worn out” or broken down and this is relative to each person.
In the case of your specific example with the N1 layer it would clearly be less durable than your second alternative at your weight and in extreme cases it could be a matter of months or on the other end it could be a decade depending on your specific circumstances. If you are past 90 days or so and still “symptom free” and there are no subtle signs of pain or discomfort then it would most likely be measured in years.
Phoenix