My MPG has stayed identical to what it was before the WP change. As I mentioned in my post, I also replaced the thermostat and temp gauge sender unit using Motorcraft parts.
As far as performance goes, I feel no difference whatsoever. This is good, since I wasn't looking to get any gains out of the WP swap. If the EEC-V was that sensitive to a WP swap, I'd be really concerned in re. to its intelligence (either too smart or too dumb or a bit of both).
My main reason for posting was because I am concerned (like you) that the computer might not be going to closed loop operation and hence run richer and blow through O2 sensors and cats at a much quicker pace than before the coolant system service.
FWIW, I do feel that the max heater output is a little less (5-10%) than it used to be. Hard to tell, the lowest temp around here is usually around 40F.
