You only read part of it. Use an appropriate valve and your toilet won't overflow whether it has 20 psi on it or 120 psi on it. It will fill more slowly at 20 psi than at 60 psi.
And I disagree on the 8psi. For most carbs we use here, 8 psi is pushing the limit of what the inlet valve can hold off - the bigger ones of course are worse.