People have achieved very fast times with many different systems. I believe the current world record of just over 12 seconds for a deck was done via PAO. The best way to get faster is, surprise, practice!
Adding complexity is usually not the answer to improving speed and accuracy unless that complexity allows you to compress your information into less imagery. When you talk about encoding more things per scene like adding an element with a PAPO, the thing to realize is that you aren’t really gaining anything in terms of better compression, simpler images, etc.
Think about the ELEMENTS of a mental image or scene. These elements are the smallest piece of an image that encodes information. These are the P’s A’s and O’s.
No matter how you encode a scene, if each element represents a single card, you’ve still got a 1 to 1 encoding compression. You could build a scene out of people, actions, objects, emotions, colors, adjectives, tastes, and textures, all combined into a scene containing 8 distinct elements, but you still have to accurately encode and decode each element individually. You still need 52 elements to get through a deck. Plus you’d have to spend a lot of time learning the associations for each of those element categories to their designated card.
Rather than adding more types of encoding elements, maybe try to just push your speed and fluency. Set a metronome and try to push through each card at a pace thats just a little bit faster than what you can manage right now. Once that gets easier, keep increasing the speed. Force yourself to go quick and soon that speed will feel normal. Incremental progress is your friend! You can do this both for practicing the speed at which you can see a card and visualize its element, and the speed which you go through a deck and actually try to memorize the sequence.
At your current success speed of lets say 10 minutes for a deck, that means you’re working on each card for about 11.5 seconds. About 34 seconds for each PAO scene.
In order to memorize a deck in 4 minutes your pace needs to improve to about 4.6 seconds per card, about 13 seconds per PAO scene.
Break that down further and figure you’ll need about 2 seconds to see the card and recognize its associated element, then another 2.5 to integrate it into a visualized scene.
If you work your way towards those benchmarks and set a realistic timetable for improvement, you can try to set some reasonable goals for yourself and watch it progress.