I want to add
i915.i915_enable_rc6=1 as a kernel line as described here but I'm unsure where/how exactly.
If you've updated to grub2, edit /etc/default/grub
add i915.i915_enable_rc6=1 to the following line(s) (ensure they are not commented)
GRUB_CMDLINE_LINUX="i915.i915_enable_rc6=1" # for both recovery and normal mode
GRUB_CMDLINE_LINUX_DEFAULT="i915.i915_enable_rc6=1" # for normal mode only
Then update the grub.cfg file, typically
grub-mkconfig -o /boot/grub/grub.cfg
Determine your grub version and check the Arch Wiki for additional details. Many users, myself included, switch to Arch because of their excellent documentation.