Parallel pumps are only effective with low restriction components for increasing flow as head does not increase and it is head that is needed to force more water through a block, yes you will increase the flow through the block a bit with pumps in parallel but not by nearly as much across all situations as if you had them in series.

Vapor on that prelim figure I guess you have mislabelled your y axis hopefully that is Core temp not a deltaT value! Oh and don't forget to factor in heatdump from the pumps into the situations while not a huge issue if you move from 3 pumps running at full blast ~60W to a single pump at ~10W you will obviously see a difference in water temps and heat dissipation through the radiators. So perhaps a comparison value of core temp against water temp entering the block would be more appropriate as a measure of performance?