Hi. My system is very slow and unusable. I am tired of this nvidia card, but
this bug appeared since version 17. After reboot all seems to work well, but
after sometime, system freezes every few seconds for a few seconds. 

When you type in console, there is a noticeable delay when typing, when you
watch vidoes, every few seccnds screen freezes. Totally unusable, until reboot.
After reboot system works well for a few hours. This happens long time, after
mesa 17 was releases and mesa 13 was disappeared from gentoo portage. Mesa 13
was the only well-working setup. 17 was in beta, I tried it and then reverted
back. Now I don't know what to do... nvidia drivers also don't work well.

I tried mesa 18 but sddm does not start.

My setup: 
mesa 17.2.8 (considered latest stable in gentoo)
Gentoo hardened 4.9.24-grsec
Nvidia GTX 660 (GK106)
nouveau.config="NvGrUseFw=1" (and a few blobs, without this system freeze and
image is damaged)
everything else is updated to latest ~amd64 versions.
4 monitors

Please help.