[Schurkey]

The 850 Edelbrock RPM Q-Jet used the same dimensions as the other "800 cfm" Q-jets.

A 750 Q-jet will support ~600 horsepower. If you need more primary throttle than the 750, there's still plenty of 800s ready-designed and ready to be rebuilt and calibrated. No point in reinventing the wheel. Yes, sometimes a bit more primary throttle is useful on certain applications.

I've got zero experience with the big Thermoquads; but they sound like fun.

Originally Posted by carbking

To compare CFM ratings, one needs TWO numbers.....CFM and rating vacuum.

...and whether or not the rating is for wet or dry flow. There's probably more still to be specified--intake air humidity and temperature, for example.