I agree with Anonymous, i had done a test on a 64GiB RAM Ryzen 7 2700x (16 threads on 8 cores) and when Rendering (CPU is max used) the I/O on the LUKs SSD drops down a lot.
Most if using not AES, using cascade (LUKS over LUKS) with algorithms that must run on the CPU while no CPU is free to be used since it is been used on Rendering.
Identical situation for fast transcoding MPEG2 (DVD VOBs) to MP4, cpu is maxed out so there is no CPU free for LUKS.
Just a tip: If we would talk about fast NVMe (3000MiB/s write) the drop down is the same, you get a few megabytes per second writes when CPU is being used intensibly.
And that tested on a 4.35GHz Ryzen 7 2700X (8 cores / 16 threads) with 64GiB RAM 3200MHz.
Another Tip: AES is broken and has back-doors, worst if it is the hardware builtin "Intel" processors AES (or also worst disk drive internal AES), to be safe do not use AES for LUKS, neither use hard disk drives (HDD and/or SSD) with built-in hardware encryption, if you do not use ATA-passwords on them any one malicious can launch a fast command (in less than 0.1s) to it and activate a ATA-password change (from empty to non empty) and on next power down your data is hijacked, you can not access that disk without that ATA-password.
Software encryption is against speed, hardware encription is not even safe.