500cfm Summit carb on 318

Just like anything it probably needs to be jetted. But 500 is maybe a tad small for 5.2 litre motor
There's a carb shop in town and he keeps telling me a 500 is to small, but I don't listen :)
The best this car ran was when I had a Eddy 650 AVS 2 on, great acceleration, ran great. But I kept thinking I don't need a 650, I rarely get over 4500rpm. All the calculators say 500cfm or less is plenty, but none of them really ran that well or got better mpg. We do a lot of cruising so (Route 66 couple years ago) so I'm always looking for something to get better mpg. I think I've exhausted all my options out there, I'll play with this one awhile and decide what to do over the winter. :rolleyes: