On the street; with street-friendly gears, and street tires,
it hardly matters, especially with an automatic
because;
Top of Second gear is gonna be around 85mph@5500
At 65 still in Second, with 3.23s, at WOT, your rpm is gonna be about 4100, which mathematically, means a 500 is more than the engine needs.
Your engine, will only pull whatever it needs thru the carb, NOT what the carb is rated at. So whether your carb is a 600 or a 1000, if all your 383 is able to pull is 455, then that's what it's gonna pull thru either carb.
Having said that, the bigger the primaries are, the less snappy the throttle response will be at the lower rpms, especially as the cylinder pressure drops.
For you
If I had the choice, I would go with a spreadbore, and then it don't much matter what you run, as long as it is at least equal to what the carb-formula spits out, which in your case is 455cfm at 4100@100% efficiency, or 555@5000@100% efficiency..... more like 470@ 85%
Now
if you have a big cam that is still making power at 6750, that would be a 750, and I'd go with a double pumper, cuz I'd be pushing 190psi cylinder pressure, or more, and when I nail it, I'm expecting gobs of tirespin....... but maybe that's just me, lol.
but, one more thing I gotta say, I tried a 600VS Holley on my 367, and it sucked bigtime. So I reworked it for fuel-economy, and in that mode, it does pretty good. But, I wouldn't ever recommend that Holley-carb for any V8, except maybe a Chevy, lol.
At age almost 72 now, I'll probably never again run anything but a DP.
If I want less tirespin, I know how to Not floor it and I don't need a vacuum pot to help me on the street. I learned real quick that tirespin was a sick thing to play with.
But, if fuel-economy is on the Table, sometimes, with a DP carb, the secondaries do open too early, and that usually costs you mpgs. Like for merging into traffic or for passing. Say you need 250 hp for what you want to do, and the primaries could easily do that. But with a DP, you cannot get 100% primaries at 0% secondaries, cuz the secondaries begin opening maybe at 60/70 percent, and I always streetjet the secondaries a lil fat. Thus, when I dial in 250 hp, my secondaries will be flowing fat, and costing me mpgs, compared to say an AV secondary, set-up for these kinds of situations, especially say, a spreadbore.
If your engine makes plenty of low-rpm vacuum, I would also go so far as to recommend a metering rod type carb. But don't put that thing on a 292 cam, lol. But that thing will work great on a factory 2bbl cam. Which I guess, is one of the reasons why a Thermoquad was such a great option. It had everything a streeter could ever want, including the oh-so-intimidating, roar of sudden-defeat.
Yeah so, I use that carb whenever I have the option.