I made a quick test on my AMD Ryzen 5 4500U Dell laptop using my Sony a6300 4K video 3840 x 2160 MP4/MOV H.264 4:2:0. I have the H264/HEVC hardware accelerated decoding/encoding for AMD enabled and the mercury payback engine GPU OpencCL enabled too. I made 3 tests: 1st test, I added 3 accelerated effects for the same video on the timeline, Brightness/Contrast, Color balance (RGB) and Gamma correction. 2nd test I used 1 accelerated effects FilmConvert Nitrate. 3rd test I used 1 accelerated effects Lumetri color.
The 1st test, yellow render line, playback was smooth and had no drop frames, the 30secs video was exported in 50 secs, Avg CPU 13% & Avg GPU 50%. The 2nd test, yellow render line, playback was smooth with no drop frames and export time was 1min & 2secs, Avg CPU 12% & Avg GPU 45%. The 3rd test, red render line, playback was a disaster, choppy and freezes, export time was 7mins & 23secs. Avg CPU 80% & Avg GPU 7%.
ALL 3 videos were exported in H.264, render at max depth, CBR bitrate 100 and max render quality.