I don't know a lot about turbo, but my guess is because you have more aggresive cams (compared to standard anyway) and combined that with a big turbo, you've effectively pushed your torque and power to the higher RPM range.

You know, the more aggresive cams you have, the less torque you have in the low RPM range and combined that with a bigger turbo which, this is what you get.

Just my guess...