how much head flow to justify dually carbs?

I ran the weiand street ram on 2 seperate BBs with 600 holleys, One was a 451 lowdeck, the other a mild 440 with stock replacement pistons, the 451 was unstopable over any other single carb i tried, just this pst year it got a pair of 660s & the power is even better all across along with the 60ft., It gained close too 2 mph & dropped a solid .2 over the 600s. The 440 had tons of torque as long as you stayed out of the secondaries, I'm guessing the compression & volume didn't match up, i'm sure a pair of 450s or 500s would've been better, but either way, both these engines had irons heads, Low end torque IMO was better then a single carb. Those were my results, others may very.