Hi doshspy,
Assuming that the type of latex was the same with all your options … the biggest difference outside of the return or exchange policies would be that more individual layers can provide more options to customize the mattress (or in some cases add some additional complexity) before and after a purchase.
Again … this would depend on all the parts of your personal value equation that were most important to you including your confidence that the specific design would be a good match for you in terms of PPP along with the importance of the options you have available if your actual sleeping experience indicates that the specifics of the design doesn’t work as well as you hoped for. Your confidence in the suitability of the design would also be affected on whether you had tested a mattress locally that had the same or a very similar design. These are all parts of the pros and cons of each of your finalists when you are down to final choices between “good and good”. At this point there are really no mistakes in terms of quality or value but each person may make a different choice based on what they believe would be the best choice for them.
This is a question that I really can’t answer except to say that it would depend on your combined testing experiences, your discussions with each manufacturer you are considering, and most importantly your conversations with your wife. It may also depend on which of you has the strongest preference or is more sensitive to different types of combinations. In our home … if there are compromises involved regarding anything involving the bedroom furniture or environment … we have happily agreed that my preference counts a “little less” than hers :).
The comfort layer will be responsible for much of the “feel” and the pressure relief of the mattress and the deeper layers will have more to do with support/alignment (although of course they are also a lesser part of the “feel” of the mattress as well).
In almost all cases I would say it would be long enough yes although there will always be some people that may feel they need a little longer for various reasons that are more unique to them.
I’m looking forward to finding out what you end up deciding but for what it’s worth … final choices where there are really no bad options any more and where there are no clear winners between your finalists can sometimes be more difficult than all the rest of your research and testing combined. 
Phoenix