Turns out you can do this by altering the following values via Terminal:
defaults write com.apple.dock springboard-rows -int 8 defaults write com.apple.dock springboard-columns -int 8
For these changes to have effect, you’ll need to restart the Dock. You can do this via Activity Monitor or by typing
Here’s what mine looks like on my 16″ MBP:
So much better than the massive icons that come by default.