Hi cityslicker561,
You can’t really measure support in terms of ILD (because support and firmness aren’t the same thing) but “IF” two layers of latex are the same thickness AND the same ILD and one is Talalay and one is Dunlop “AND IF” the ILD in both is measured the same way (which often isn’t the case) … THEN they would be the same firmness if they were both compressed by 25% (where ILD is most often measured). If you compress the layer more than 25" (which would often be the case for a comfort layer) then the Dunlop layer would feel firmer to most people because it has a higher compression modulus which means that it gets firmer faster as you compress it more deeply than Talalay. This is why most people will tell you that Dunlop feels firmer. If you were to compress them less than 25% then the Dunlop may feel softer because of the difference between the shape of their response curves. Because of the variables involved with different types and blends of latex they are not directly comparable in terms of ILD (see post #6 here) and ILD itself is only one of several specs that affects the sensation or perception of softness (see post #4 here).
Both Talalay and Dunlop come in a wide range of ILD’s from very soft to very firm and both are usually manufactured in cores that are about 6" thick (although some are a little more or less) but can be cut into any thickness less than this as well.
There is also more about primary and secondary support and their relationship to pressure relief and firmness in post #4 here and in post #2 here.
If the blend of natural and synthetic latex is the same in both and the Dunlop isn’t certified organic then Dunlop is usually less costly yes.
I personally think that it’s mostly pointless to try and describe one as being “better” or more durable than the other because there are many variables involved with durability and the useful life of a mattress as well (see post #2 here) but both have a long history of being very durable and lasting for many years (see post #9 here).
Phoenix