On the stamped vs cast impeller water pumps:
Crawford announced in 2011 their new "secret" to success high flow water pump. They have a pic in this article and talk about it, about half way down:
http://www.superstreetonline.com/how...s-engine-tech/.
To save you the click:
Q: You came across an interesting finding on the factory water pump. Would you care to disclose this information?
A: The water pump (front, right) is a cast turbine that flows more water, whereas the OEM piece (rear, left) allows for water to bypass the blades and does not flow as much water. It is one of our trade secrets of engine building and you are first to hear about it.
http://image.superstreetonline.com/f...water_pump.jpg
If you Google Crawford High Flow Water Pump you'll find multiple threads about it on NASIOC and IWISTI.
Then the community figured out it was nothing more than the Subaru OEM old style cast impeller pump. I think Crawford has now discontinued sales of their high flow pump. It's not on their web page anymore and RallySportDirect shows it discontinued.