I remember a little while back reading about how audi had done years of research to come up with a little plastic baffle that preferentially sent the cooled water from the water pump to the higher side of the bores first in an effort to reduce temperature differences from the top of the bore to the bottom. In so doing, they increased their MPG's by something like 1.2% which yeilded far more in emissions credits than the program cost and also cost far-far-far less than developing a new block with improved coolant flow paths.
The main benefit of keeping the bore evenly cooled was improved ring sealing that accounted for lower fuel consumption and less blow-by which help with oil consumption and keeps key parts of the exhaust alive longer. The original temperature difference was in the mid double-digits from what I recall, and the baffle got them into single digit territory.