Hi FurmanSK, try
just to verify that my intuition is correct, I reused the legacy bootloader and ported a couple of kodi patches that are in Omega that increase performance.
Remember that decoding 4k contents and smooth UI at 4k resolution are different. So please try with a lower UI resolution, and let kodi player switch to 4k when needed.
edit: if works share the output of cat /sys/kernel/debug/clk/clk_summary