Pressure (head rate) matters more than volume.
WW will make much better use of a pump such as the MD20rlz than a higher flowing version of that same pump, MD20rlt which has much higher flow but a much lower head rate (pressure).
The sustained temp of a system is what matters. And no matter the volume of coolant the system will reach it's balance point and stay there. A large rad does increase volume of coolant some, and a large rad lowers temps, but added volume in a large res means nothing.
The value of a res is in ease of trapping and removing air from your system.
And welcome to pro cooling.