Hi bbqBiker,
Thanks for the kind words 
There is a discussion of some of the pros and cons of split layering in post #2 here.
Most of this deals with the question of “will I feel it” though rather than your question about durability although they are related. In general there is an “edge effect” with foam because the edge of a layer that is not glued doesn’t have any material beside it on one side to moderate the compression directly under the body. While I don’t have any links to “scientific evidence” that has tested this directly, because of the “stickiness” of latex and also because most manufacturers will make sure that the ticking/quilting used (or alternatively a thin layer of foam over the split) is thick enough to even out the compression in the area of the split, any difference in durability is not likely to be significant enough to be relevant. I do know that in many cases … the “testing” of different mattress designs or ticking/quilting combinations used by manufacturers that offer split layers before they offer the mattress to the public specifically includes the effect of the ticking/quilting or other layers on any split cores.
Phoenix