I have tried installing the new build (9879) after doing a complete rebuild of my 8.1 system, over a clean 9841 install, and even as a clean 9879 install. Every time the system is unusable due to a Blue Screen.
I get the message error 0xC1900101 - 0x30018 and WHEA_Uncorrectable_error. I cannot get any more info from the dump files. I have tried disabling some devices to find an answer, but have been unsuccessful.
Since some are saying there will be no more builds this year, it looks like my preview testing has come to an abrupt end on this system...
It is a little strange a Windows 10 builds would leave around 30 unidentified devices in the Device Manager, but I suppose Microsoft has not yet added the X99 chipset to its archive of drivers.
If anyone else is running an X99 system with this build, please advise.