Big difference is it doesn't buck as much and the low end response is much sooner. Peak doesn't actually change much but the response from 2000-3000 RPMs is dramatically improved. It's much smoother running as well.
It really made a big difference in driveability. It's so much easier to zip off the stoplight, or merge in traffic. The lag is virtually eliminated b/c of the low end torque.
I had a problem with hesitation throughout the RPM range. It was a lot smoother with Stage 1. Of course, that made me want Stage 2. Honestly I think the Stage 1 improvement was bigger than the Stage 2.