I'd believe it. Even with my old non wg turbo and the wg Banks only doing 7-8 lb it felt like close to twice the power. I found that the turbo lets me run a gear higher than I would before - that is a hill I'd pull in 2nd at ~25 I could do in 3rd at ~45 with the turbo.
If you figure that 15 psi of boost is basically double the amount of air being pumped in, you should be able to burn double the fuel for roughly double the net power. (minus losses of course). So 10 psi should be about 2/3 again as much air/fuel, or theoretically about 100 extra hp. Not actually going to see that much, but ~80 is somewhat reasonable as an ideal conditions max gain. I think an extra 50-60 is more reasonable for real world use, but then the engine isn't going to make the rated 160-170 in real world use either, so you're still going to see a ~40% increase in useful power.