To test the Y-pipe, I performed two power runs before and four more after. The temperature was about seven degrees higher and some amount of humidity, but I haven't bothered trying to correct the figures. You can see the after runs are a bit higher than the before in spite of the different conditions. I averaged the peak power numbers to find the power gain was about 5.5 bhp. After correcting for driveline loss, that means about 7bhp "at the crank."
I would expect a bit more in less hot conditions, and my first power run was four bhp more than successive runs, which could indicate heat sapping the engine power. Regardless, the exhaust performs as expected. I compared the highest before and after power run to show where the improvements really are. Through all of the RPM range there are slight improvements, but the real change is from 4800rpm to the redline. Overall, the peak power went from 194.5bhp @ 6200rpm to 200bhp @ 6300rpm. While I haven't decided if I'm going to change out the resonator and muffler yet, I do expect that after getting the ECU reflashed that my top end will be substantially stronger than stock. Now I just have to figure out where I can do a top speed run once the 146mph governer is removed! :)