Looks good...
Yes, many variables affect final temp - radiator airflow is only one. IMHO, if you are not seeing any measurable change in temps when slowing the raddy fans down by roughly half, then the radiator system is not the limiting factor in your cooling system. Something else, such as overall flow rate, is holding you back.
Try measuring your system flow rate: connect a large (constantly filling reservoir to mainatain constant level), disconnect your return line and measure how long it takes to fill a 1 gallon (or 5 gallon) bottle => GPM or GPH (or liters if you prefer)