Dyno comparisons are VERY good on the same car, same dyno, and similar conditions (temperature, humidity, etc.) to see the effect of performance upgrades and tuning.
Dyno comparisons of different cars across different dynos under different conditions are challenging at best.
The most important info is the CURVE and NOT peak HP.
Forgive my crude graph below, but it is a good illustration of my point.
That said (whew, I feel better now).... according to Whipple, the new rotor shape is more efficient - providing two main benefits. The new screws can produce the same boost with less rotor RPM. If I understand correctly, the 19 lb size Gen1 pulley will now produce 21 lbs of boost and allegedly at nearly the same IAT's as the 19lb on the Gen1. So, you get the better belt wrap of a larger pulley (less chance of slipping) and you get better air inlet temps.
In short, Gen 1 and Gen 2 can both produce 21 psi of boost. The Gen 2 will do it with a slightly larger pulley and better inlet temps.... giving a better margin of safety for tuning. I would expect HP to be similar - but the Gen 2 will let you be a little more aggressive with tuning which can translate to more ponies.