A vote for the cast impeller
 

I know this has been beat to death but this is my story and I'm sticking to it.

61 with the old four bolt pump. PO had overheating problems. Vapor locked (a vapor return line fixed that) but it would run 200-210 and it didn't take a very hot day to cause that. I pulled the 195 stat and put in a 185 which helped but I still like to be under 190. Added a shroud and clutch fan which still didn't get me where I wanted to be. A few years ago I had the engine out to get things cleaned up and looked at the pump but never really noted which one it was and quickly forgot. Cast or stamped impeller - I didn't remember.

So I picked up a rebuilt pump and put it in. Now it runs a nice 180-185 (still the 185 stat). Even on 90-95 degree days. Pull off the road and let the revs drop down in town and it will go to 195-200. But you expect that.

The pump I took out is on the left and the one I put in is on the right. Note that although the stamped impeller has more blades it is also a smaller OD which I think allows some loss of efficiency at the blade end. Can't say how the cast impellers with the shorter backward angle blades would perform.