Hi janstadt,
I haven’t talked with Neal for a few weeks and we were talking about him offering Talalay but I didn’t realize that he had it available. Thanks for the heads up 
The ILD ratings for different types and blends of latex aren’t directly comparable (see post #6 here) and two layers of the same thickness that use different types or blends of latex that are the same ILD may not be the same softness so the 25% ILD ratings of Mountaintop layers (they also have a 40% ILD rating) wouldn’t be the same softness as a Talalay layer of the same thickness and ILD.
Neal would have much more personal experience about how they would compare and he would be a much better source of guidance about this than I or the other members here that don’t have the same experience comparing them as he does.
When you can’t test a mattress in person for PPP (Posture and alignment, Pressure relief, and Personal preferences) then the most important part of a purchase decision and your most reliable source of guidance to help you choose your layers will be a more detailed conversations on the phone with each manufacturer you are considering. They have more experience with their own mattresses than anyone else and can help “talk you through” which of the options they have available would likely be the best match for you based on their knowledge and experience and the information you provide them about mattresses you have tested and that worked well for you as well as more about your body type and sleeping positions, and the “averages” of other customers that are similar to you.
Phoenix