Not yet, I just put them on yesterday. I haven't been keeping track of the gas mileage, since the odometer doesn't work with the engine off and coasting and it takes a mile for the GPS to start working. It seemed to accelerate faster down the slope into my road, I had to brake, but it was just repaved and now super smooth. 10% of the drag on a car is from the front tires.
I don't know what rectifying effect is, but it might have to to with the body on the Probe IV is so low to the ground that the angle of the tread to the pavement is quite acute. My car rides quite a bit higher than stock due to the over size tires (2050 rpm at 65 mph).
The air flow forward of the front wheel is flowing outward somewhat because it is deflected around the body of the car. This can be seen by the streamline streaks left by dirty water drops on the belly pan underside. Also by this:
it's also interesting to watch the spray from tires during a rain on the freeway