"Theoretically" going to 7000 needs 775cfm and 7500 needs 830cfm, but as Brenx said, there are good results to be had with the 750hp....not to say the BG's or Proform's wouldn't perform well either.
The BG King Demon is a nice piece of kit.....but as always comes at a price (US$1100). You can change the CFM of the carb by inserting different sleeves. One carb fits all
The Proform, from what I can tell, is just a copy of a 750HP anyway? (with funky anodized metering blocks). They're US$50 more that a Holley equivalent.
It would be nice to see back to back dynos vs "average" hp and tq up the rev range vs peak numbers.