As for data you requested, at the 50k mile thread, someone stated having 770rwhp with a 4.0ltr Whipple. I recently had a new GenII installed and dyno'd it at 726rwhp, while right before the install we did a baseline dyno at 621rwhp on the, then, existing set up of pulley&tune. I've been told that my before/after rwhp readings are very typical from such mod. As it's been said many times by others, I was perfectly happy with the pulley & tune, now I have a slightly bigger smile with the Whipple... Only if there are so many LEOs on the road here in CA.
I opted for the GenII because I didn't want deal with the potential fuel upgrade requirement.
Ed