850 cfm proform carb on 318!!!!

FWIW, I have a fairly stout 360, ~375HP. I have had 600, 670, 725 and 750cfm carbs on it. By the butt dyno I don't feel any difference in top end power between using the 670, 725 or 750 but either the 600 or 670 have it all over the bigger carbs in off idle through mid range in throttle response. I settled on the 670 as the best all around carb for my engine, plus it gets 5 mpg more than the bigger carbs.

I think I read the article you are referring to. If I recall the dyno runs started at 3500 rpm and went up, no info in the rpm range a street car speeds the majority of it's time. Dyno runs are done at WOT so they don't tell you anything about how the engine is going to run at part throttle when you are mostly running on the idle and transition circuits.

Another thing to consider going to a carb that is much larger than what the manufactuer recommends for an engine is going to require a lot more tuning to get it to run exceptibly. It won't be a main jet change, you will be playing with air bleeds, squirters and likely the emulsion jets on the metering block.