One thing many missed out from the discussion, over-inflated tyres can be dangerous as well.

Over-inflated tyre provide you less traction and can cause safety issue as well.
Not to mention causing damage to the suspension as well as early damage to the tyre itself, which cause you more money to repair/change afterwards.

Don't be penny wise and pound foolish, aka try to save a few penny then loose a few pound.

There is reason, why optimum tyre pressure is recommended.
If over-infated pressure is good, then you see car manufacturers should be recommend must pump tyre over xx psi already, not xx~yy psi.