I have some aftermarket tires on mine -- 205/50/16"s. Since these are a bit lower profile, they need slightly more pressure even to get up to the same effect, as they will flatten out more at 30psi than the stock tires. I'm running them at the max sidewall 44psi. However, since these are wider, and there's more rubber on the ground, I find the effective difference in mileage between tire pressures is much greater. They're also more sensitive to heat than the stock tires, as far as effect on mileage (hotter is better).

However, more noticable than the effect on mileage however is the increase in handling. At the higher pressure, the tires seem to hold up much firmer around turns -- they also provide more steering feedback, those two variables alone would be worth the extra pressure. The only drawback is that they are noisier, though I have responded to that by adding a bit of sticky vinyl-foam insulation to a few panels on the car to absorb the road noise, which has been fairly effective.

These differences are more profound, for sure, and there are diminishing returns in mileage above about ~40. However, raising it from 30 to 40, in both the older tires and especially in the newer ones, coast-down distances from spots I drive on every day are longer -- clear evidence that rolling resistance is lower.

 

I run 40psi all around. The road noise is more noticeable, but I love the handling and gliding.

Mike, where did you install the insulation on your car? Any pics?