The most efficient method is to have as few security checkpoints in the airport as possible, thus maximizing the number of metal detectors and X-rays machines for one checkpoint. An express line is useless because almost everyone has something to put in the X-ray machine.

When there are lots of checkpoints and few machines per checkpoint, some checkpoints have lots of people in a long line while other checkpoints sit idle. Having fewer checkpoints minimizes the difference in wait times, thus increasing overall efficiency. Even if all checkpoints have a wait, at least you equalize the wait for everyone.

Naturally, it would cost a lot of money to re-design the security checkpoints. But until then, at the very least, there should be no requirement that your boarding pass match the gates nearest a particular checkpoint when more than one checkpoint has airside access to your gate. That effectively combines multiple checkpoints without any construction work.