What carb do I need to get?

I'm putting a 4 bbl carb on my slant six.
I've been looking and I am leaning towards a Holley just which model would be the best application for street usage.

I am buying an offenhauser intake this weekend.
Already have headers and exhaust system. Can't figure out which model would be best.

390cfm or 600cfm
Any other options to please.

Any tips or Tricks are appreciated as well