I wouldn't take the readings of the stock temperature gauge too seriously. They are notoriously innaccurate. "N" on one gauge may be the same temperature as "O" or even "R" on another.
Unless the thermostat has been changed to a drastically different temperature rating, the new pump should not have much of an affect on engine temperature. An 195 degree F thermostat swapped out for an 160 degree unit can make a difference in performance and emissions, especially in cold weather. Also, a cold running engine is subject to more wear since typical motor oil additives work better at temperatures above 180 degrees.
I would not woory too much also about carbon deposits based on changing the water pump alone.
