I have no flow data on the D0 heads. I think they are very close to the stock E7 heads though. Without flow number the desktop dyno is about worthless.

I have used the powerheads E7 heads. The performance went up a very noticeable aamount. It went from like 14.8 in the quarter to 14.1. Low end wasn't really hurt but the gas mileage was horrible. The GT40P heads should give you better power and efficiency but you won't get as much power as the powerheads.