Obviously dependant on airflow thru the rad, but... assuming a fan is chosen that provides enough airflow to allow the rad at a given flowrate to disperse the amount of heat being generated...
A 120.1 rad will cool a fully block'd (CPU, NB, 2x GPUs) succesfully.
A 120.2 rad will cool it succesfully, but return lower temps.
A 120.3 rad will cool it succesfully, but return even lower temps.
Simple as that really. Bigger the rad (assuming identical fans are used and just quantity of fan increased), the closer the final temp of the item(s) you're cooling will be to ambient (ie: the smaller the DeltaT)