Updating gentoo-sources to 3.10.7 and running 'emerge nvidia-drivers' results in a compile stop containing the message that NVIDIA only supports kernel versions < 3.10
Possibly a newer nvidia driver does not have this restriction.
nvidia-drivers-325.15 (currently latest version in portage) officially supports 3.10 so unmask it until it gets stabilized.
If what you wanted was to call a stabilization bug on 325.15, reopen it saying so.
*** This bug has been marked as a duplicate of bug 447566 ***
On top of that, some people experience that 325.15 with the 3.10 branch does not work properly together; so, you are advised to use the kernel from the 3.9 branch if that is the case.
Use nvidia 319.49, which supports kernel 3.10