Stock Water Pump reliability.
Electric pumps free up HP because the engine no longer has to turn the impeller, but at the cost of less flow at higher RPM versus the stock one.
Stock pumps are very good and flow more as RPM increases.
Your turn it by hand test is silly, the waterpump turns faster than the crankshaft, now try and turn it even 600idle rpm by hand not even accounting for the overdrive. Do you have a better understanding now?
How long a mechanical lasts can't really be said, reman shops do varying levels of quality work. Pick a retailer you like and trust their warranty.







