Wouldn't it be more efficient to just play Act 3 over and over?
No, some people fall to this thinking because they overvalue the ability to carry the 5 NV even though the sacrifice they're making is that they have to clear low density, low exp areas as a result. It's much better to cherrypick the highest density areas in A3 and just clear those over and over even though you have to re-stack NV every game.
BTW, those instructions from Diablo Wiki are a bit off. You first want to checkpoint outside of Azmodan's lair so that you begin every game from there. Then it goes as follows:
- Core of Arreat (backwards)
- WP to Tower of the Damned 1. Make 1 circle.
- WP to Arreat Core 2. Clear to the end and enter Tower of the Cursed. Head to the WP.
- WP to Bridge of Korsikk. Make 1 circle.
- WP to Keeps 1. Enter Keeps 2. Clear to the end or as much as you can clear in one sweep.