hey, i'm using 4070ti super on my 4k display and I have really simmilar experience, although my average hotscreen performance is around 50fps, with both screen recording and body detection rates in 40-50fps range, despite setting fps presets for normal (60) or high (120). - higher fps cap allows for bigger variation of performance, as overlays frame rate range from 40 to 80 fps
neither mine cpu/ram/gpu performance seems strained - 10gb free ram space, cpu under 25% usage, gpu memory under 20%, yet the experience seems like it's on the edge (lol) of it's capabilities