The split had been established at something in the 350,000 year range based on the fossil record.
Just in the last week or so I saw an article, I think here on FR, that suggested a split a little earlier based on genetics. They placed that in the 400,000 year range.
I would take that with a grain of salt to start with, until more data comes to light but it seems that the evidence is heading toward an early split at this point.
Certainly the mtDNA tests that were done suggest no close relationship or interbreeding.
In the back of my mind, is the memory of an article--popular science stuff--that explains modernity as the result of infantilization, with the moderns retaining the relatively large skull of the infant. That would make the Neanderthal types our ancestors and collateral cousins.