In case of CPU there's another challenge in how tiny actual heat producing areas are.i have been wondering about, what if i added the cpu to the loop. Another 360 rad maybe thicker?
While GPUs are all big chips with heat production happening quite evenly around them, CPUs have heat production concentrated on execution units of cores and those are really tiny in size.
And there's limit at what rate heat can be spread around and transferred from those to cooling system.
So with such high energy output, it's hard to lower temperatures of CPU cores.
Even in case of own cooling loop.