500cfm Summit carb on 318

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 an 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:
The best it ran ever was with a 650 eddy, so you’re going to let it run like crap and stew over what to do and keep using a 500? That doesn’t make sense. Your car, 4 bolts and a fuel line could fix it, but why don’t you call it quits for the rest of the season and decide over the winter what to do……..