The following excerpt from the 1972 Ford OHO (Off-Highway Only) publication shows water flow rates of various Ford water pumps. Stock 351-C/400 (p/n DOOZ-8512 A) with straight blade impeller flows 78.8 gallons/minute @ 5000 rpm using 5.4 bhp. (Ford Note- cavitation begins at 5000 and becomes severe at 6000 rpm). At 7000 rpm, flow= 85.9 GPM using 12.4 bhp. Note minimal extra water flow while using 2-1/4X more power, due to severe cavitation.
Stock Cleveland pump with curved Boss 302 impeller adapted & reduced in OD= 42.1 GPM @5000 rpm using only 1.6 bhp. Same pump w/cut-down Boss 302 impeller flows 60.4 GPM @ 7000 using only 3.6 bhp with no cavitation to 9000 rpm. But some low speed overheating may occur on the street with such a pump. Chart doesn't say if the numbers were free-flow or mounted on an engine with the usual flow resistance.
You can get much the same effect by slowing the stock pump down with various pulley sizes. The flow numbers also indicate why a 1/4 horse electric water pump alone will not cool a street 351-C for very long regardless of its efficiency over a belt drive pump. Ford's OHO publication was only published for a little over a year and is in the POCA Archives. Lots of good stuff in there but was dropped when Ford, GM and Chrysler stopped supporting racing.