Time-depth of Indo-European

Recently I've come across two articles and a book providing evidence for the breakup of Proto-Indo-European around 8000 years bp. For instance, R. Gray and Q. Atkinson using a method of cognate analysis generate a date of 8,700 bp for a split between the Hittite branch and all other branches of the Indo-European family. P. Forster and A. Toth come up with the date of 8,100 bp for "Indo-European fragmentation", and as I recall Cavalli-Sforza reaches a similar date in his book "Genes, Peoples, and Languages".

 

As I recall from Mallory's "In Search of the Indo-Europeans" there is a different linguistic consensus, that Proto-Indo-European fragmented later, perhaps between 6000 and 5000 bp. My question is, what do you think is the correct date for Indo-European fragmentation and why?