well the way I see it.... the longer the carrier ( water) resides in an exchanger, the more heat is absorbed or expeled... this is usually the thing most people think of as a good reason why the water should flow slowly.... but not, since the longer it stays, the smaller the difference in temp between the water and the exchanger becomes. And it's the Delta-T that is the primary key to good effective cooling. Without Delta-T nothing will happen, no matter what you do.
So to actually put it more correctly, do whatever it takes to have your Delta-t's, be it between the water and block, or between the water and the radiator, as large as you possibly can....