Yeah exactly this.Generally speaking, 1x240 for both should be 'better'.
When using 2x120, you will have 2 pumps, thus occupying more space and creating more noise.
In addition, if you are doing a task which stresses only (relatively speaking) one component (CPU or GPU), then the entire 240 rad is utilized to cool, rather than just having 120 to cool and the other 120 is sitting there 'idling'. So, the entire rad is always put to full use, wasting little cooling performance.
I only went this way as no GPU blocks fit my gpu. I actually have all the gear here to custom loop from a previous build (see my avatar). But I didn’t see the point in having a 240 on my cpu only to have my gpu screaming during games.
That being said running a 120 aio for each component is working fine.
my 2080ti stays over 2000mhz and I can run my 3900x at 4.375ghz on all 24 threads for about an hour before the 120mm rad becomes overwhelmed and it hits 91 degrees.
Running a .1 undervolt for normal and gaming use and 4.2ghz all cores for multi threaded workloads keeps temps well under control with very rarely seeing the cpu hit 60 and gpu at 55 with relative silence (apart from the pumps and 92mm fan on the g12 blowing on the vrms) which all ramp up to 100% once the gpu or cpu hit anything over 50