For the record, 1.3GHZ is only 300MHZ faster then 1GHZ, your not going to see much of an improvement there. But if you really want to adjust it, you can do so by the CPU Power Manager extension.
https://extensions.gnome.org/extension/945/cpu-power-manager/
As far as boot times, this is greatly dictated by your storage memory speeds, your RAM speed, and of course, CPU speed.
When Zorin OS LITE is released, I suggest switching to that, as I feel your SPECS are a bit too low for CORE.