water pumps -plastic vs metal

[1986.5supra_kid]

so i replaced the water pump on my 2jzge and i noticed that the oem toyota pump that i took off had a plastic impeller, but the PROTO brand i installed had a cast metal one. the plastic impeller looks like it would flow more. is this something to even worry about?

 

[supraguy@aol]

I think I recall IJ once posting about certain impellors having more tendency to cavitate, but i cant recall where i saw it.