How fluent must your PAO be before it's useful for speed work?

Instant and automatic in both directions — item → its P/A/O, and any slot → the item it came from — with no conscious effort.

Encoding a deck at speed leaves no time to work out a card's person; it must appear reflexively, the way a fluent reader sees a word, not letters. Likewise, decoding a composite requires each slot to snap back to its source item instantly. Until recall is automatic in both directions, drill more — a half-remembered PAO is slower than no system at all under time pressure.

Go deeper:

• Alex Mullen, memory athlete (Wikipedia) — sub-20-second decks show the automaticity ceiling fluency must reach.