From an efficiency point of view the engine is more efficient the higher the temperature it runs at within it's allowed temperature limits.

If the engine has not come to grief in the past and now the fan no longer cuts in as often, then the engine is working less efficiently.

If the engine did use watter due to it's higher temperature and now uses less than this may be a better long term reliabilty modification.

If the car did not use any real amount of water from the cooling system with the old radiator, the engine would be more efficient than it is now.