I don't know if its the same as HVAC, but I don't understand why it would be different. You can flow your transfer medium too fast to effectively cool. In other words, you need to have the flow going slow enough to have the time needed to transfer the thermal load. Fast flow is not synonymous with max cooling. With your coolant temps being so low, you should try reducing the flow. But, I don't know AIO particulars. Is coolant temp measured in the reservoir? Just before the processor heat sink? For a fixed volume system like an AIO, there would be an optimal flow rate that maximizes thermal load transfer at the processor while transfering said load at the radiator. It would be based on the thermal characteristics of the processor heat sink, the heat pipes, etc.