How much cam did you use? What rear end gear are you using? What diameter of exhaust pipe? Why only hipo manifolds, and not headers? where are you driving the car? Around town, or on a road course or 1/4 mile strip?
It doesn't need to be that precise. Besides, the stock 289HP carb was a little short of 600, and you've got a lot more cam than that. 600, or 650, would be just fine.
The problem with the online calculators is that none of them account for camshaft lift or duration, or cross section of intake manifold, different from stock valves, or lots of other factors that affect engine performance. Don't forget jet sizing too. A smaller carb will typically get better low end performance, and a larger CFM carb, will usually be better on the top end. The 65 Shelby with a 289, got a 715 CFM carb, and my 69 Cougar with 351W got a 470 CFM (4V) from the factory.
So, I can't give you a specific mathematical equation to answer your question.
There may be something here that will answer your question:
I would just go with the 650. I prefer the Holley's, but I have Edelbrock as well. If your car is an automatic, I would stick with a vacuum secondary.....