Square-bore vs. spread-bore?

Bill Crowell said

Hey guys, what do you think works better: an Edelbrock Performer or Performer RPM spread-bore intake manifold with a spread-bore carb like a Thermoquad, or an Edelbrock Air Gap square-bore manifold with a Quadrajet or the equivalent carb?

Why do you think the Air Gap manifold is manufactured only in the square-bore configuration?

I've always wondered about this, so figured I'd ask. As always, thanks a lot.

(Corrected after RammerJammer75 pointed out my typo.)

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Until you start racing, any carb is a good carb. So long as it is well tuned.
The popularity of a spreadbore carb is low. Adapters work OK. They just have to be worked on for best return in power.
The aftermarket offerings with a spreadbore design are factory replacement intakes. With a few exceptions like the MP-M1-single plane and a Holley strip dominator or the Offy line, where the same manifold was offered in ether type. These were mostly designed for a class of racing, Allowing the stock carb. It works well for street guys in terms of a savings of a new carb purchase if you already had a TQ or QJ.

In a post by Bewy where he has done some really cool work and has shown what the dyno says it does, here are the results of a Holley Umtra HP 950, a QJ and a TQ.
I say it to damn shabby for this factory stock TQ carb. The same carb that people throw away for the expensive H brand. The factory stock version can be modified to this level.
Dyno results - Tquad vs Holley vs Qjet - tuning issue, too rich