Cfm is cfm. That doesn't change just because a radiator is in the way, the volume of air moved is the same. Static pressure is what's affected, which is the immediate presence of air in another spot. So with a 240mm rad and 120mm fan under it, yes, there will be slightly more ambient temp air shoved towards the underneath of the gpu, but once the exhausts draw really kicks in, the block of air provided behind a 360mm rad is going to move there too. You end up with @ 2-3°C difference in gpu temps at high loads, which honestly is chump change and won't affect anything.
The difference to the cpu depends on the loads. Most ppl assume temps are an attribute of the cooler, but they really aren't. They are a result of capacity vrs load according to curve. A 240mm rad has @ 200w capacity. Assume that at 70°C it hits 200w. For simplicity, assume a straight line, so at 150w load, the cpu is at 55°C. With a 360mm rad, it's capacity is @ 350w at 70°C. So with a 150w load, that'd put °C closer to 40. All that depends on the efficiency and effectiveness of the fans, that'll change from one vendor to another, and changes actual temp-load curves, but theory is same.
If you never use over @ 100w, then a 240mm is fine, there'll be no advantage to a larger capacity rad other than the ability to turn fan speeds down considerably (noise factor) which reduces efficiency of the rad, making them equal (ish). If pushing higher loads, the larger the capacity, (with equitable fan outputs) means lower overall temps.
Very basic theory of a considerably complex concept.
I currently run a Cryorig R1. 250w capacity. I7 @4.6GHz. I can hit @ 150-175w loads ±. Gaming temp 55°C, max load 70°C, quite noticeable fan noise. My prior cooler was a nzxt x61 280mm rad, @ 350w capacity. Gaming temps 55°C, max load 70°C. Cpu @ 4.9GHz, 200w+ load. Noticeably quieter and lower fan speeds on the x61, even though both are 2x 140mm fan setups.
You may or may not see much of any temp differences in normal loads, but push the cpu towards limits and you'll get far more from the larger rad overall than the smaller rad, other than just temps.