I would suspect that if you had a radiator with a fan to cool your water, flow rate would be much more important than just a closed loop with a water bucket. Without a radiator of some sort I'm sure there is such a thing as too fast a flow, but I doubt you could reach it without an excessivly large pump, as the diameter of the hoses and internal restrictions in the pump housing would limit your flow to a certain point, at which the added pressure to reach a very high flow rate would start to add heat from friction negating any added benefit of a higher flow rate.
Adapt your cold water sink faucet to the inlet of the cooling jacket and the outlet down the drain.
Ever take the thermostat out of your car and seen it overheat? Yep... The coolant has to flow just right to absorb the BTU's