Some will say the 850 is what ya need, personally I like vacuum secondary carbs. A 715 cfm works perfect on my 468 Chevy @ 5300 rpm. It gives my engine all the CFM it needs and it's pretty good on fuel consumption.
I have a 850 DB I tried...it did nothing but use MORE fuel > now sitting on the shelf for someone that (thinks) bigger is better (not always)