Hi conceptcar,
The base layers of the Radiance are 1.5 lb density but the density of polyfoam has very little to do with its firmness or with PPP … only with how long it lasts and maintain its original firmness. The base layers are also not as big a factor in the durability of a mattress as the comfort layers although this will depend to some degree on your weight, the thickness of the comfort layers, and on how much you compress the base layers “through” the comfort layers.
This can’t be predicted with any certainty outside of saying “more than this or less than that” because there are too many variables involved including your body type, sleeping position, how close to the edge of your comfort/support range you are before a mattress is too soft for you (see post #2 here), and on your physiology and where you are in the “princess and the pea” to “I can sleep on anything” range and how sensitive you are to the effects of foam softening before you cross the thresholds from sleeping well on a mattress to “sleeping OK” to “tolerating it” to finally deciding to replace it.
I have no personal experience with any of the mattresses you are considering or how they may compare with the Radiance but there is more about the different ways that one mattress can “match” another one in post #9 here. In most cases the only way to know how close one mattress feels to another one for any particular person would be their own personal side by side comparisons and/or sleeping experience. Some online retailers or manufacturers use a well known and widely available mattress as a reference point so that you can test a local mattress to get a sense of how an online mattress feels and performs but the most common reference point would be one of the Tempurpedic line. If an online retailer/manufacturer is familiar with a mattress you have tested and with how their own mattresses compare to that specific mattress then in this case they may also be able to help you make a more meaningful comparison between them.
Phoenix