I have found a water pump with a metal impeller and even though I have already installed one with a plastic impeller I just figure I would let you CEGers know that sp motorsports sells a water pump with a metal impeller

Contour/Cougar
Water Pump
Water Pump (V6) with Metal Impeller
2.5L Water Pump with Metal Impeller - water pumps on many of the Duratec V6 engines have failed by 50,000 miles or less when their plastic impeller breaks and stops turning. When this happens, water is not pumped to the radiator to be cooled, and the engine overheats. The worst part is that the temp sensor won't signal the gauge to read hot until it's too late and the engine is ruined. Avoid this costly disaster by replacing the stock water pump before 50K miles with this premium quality replacement unit that has a cast metal impeller and has proven to be more reliable.

Water Pump with Metal Impeller, All 2.5L V6 (941-K421) .... $62.50 ea.