Continuing the setup of the Chromebook I find that even Chromium is slow to load some pages, maybe I am a little impatient.
So here are the instructions to install ungoogled-chromium.
First of all you need to add the Opensuse repository to your pacman configuration file. Yes OpenSuse have an Arch repository!
echo ' [home_ungoogled_chromium_Arch] SigLevel = Required TrustAll Server = https://download.opensuse.org/repositories/home:/ungoogled_chromium/Arch/$arch' | sudo tee --append /etc/pacman.conf
Then you need to update the repository information and install the package
sudo pacman -Sy ungoogled-chromium
If you currently have Chromium installed it will prompt you to uninstall it due to a conflict, it will have No as the default answer you so must type Y/y to confirm.
There does seem to be a performance improvement and overall I am happy with the result. The only real problem is you cannot install extensions, so set Chromium up first with all the add-ons you need and then switch to the ungoogled version.