Linux Kernels tend to be very stable even at RC states. I've been testing 4.8-wip and 4.9-wip (from AMD/Xorg's repositories) at least 2 months before they even started official development, and never had major issues. Now, granted it was (probably) linux-git with the changes AMD was planning to land on these kernels, but those exactly the features I was testing and they worked as advertised
Kees Cook's overview of the security enhancements in kernel 4.9: https://outflux.net/blog/archives/2016/12/12/security-things-in-linux-v4-9/
