Have you looked into PAO combined with memory palace for numbers and cards? This may be a smart next level system for you to go for. It will require some time to build the list and drill it to get fast, but the compression advantage is worth it, in my opinion.
If you have a 2-digit PAO system built for numbers, you can use the same list for playing cards as well. There are a few threads on the forum describing how this can be done. Here’s my list as an example, using the Major System for all elements. The explanation for how to use it for cards is in the same thread, a few comments down. Post your 0-99 List here for other people to use... feel free to add - #14 by TheHumanTim
This way you can merge 6 numbers or 3 playing cards into a 3-element scene at each loci. 5 loci would be all you need for 30 numbers. 17 or 18 loci for a deck of cards. The scenes are usually easier to visualize and remember than a very long chain of single objects.