Kenth - none of the Rochester material I have gives a reason for changing from the vented gaskets to the solid gaskets on the outer carbs.
I will hazzard a guess!
Since the reason for the vented gaskets was to alleviate throttle area pressure blowing additional fuel into the intake past the slightly open throttle plates during hot idle conditions; if one looks at the outer carbs, the throttle plates are tightly closed at idle and off idle. Therefore, there would be no benefit in using the vented gaskets on the outer carbs.
If you remember, you corrected me on these gaskets in these forums a few years ago. I was using the early listing for the bill-of-materials. After our post conversation, I have switched to the solid gaskets on these carbs.
There were never any complaints about using the vented gaskets other than why; to which I then responded with the 1957 Rochester/Pontiac bulletin explaining their use.
Personally, I don't believe there would be any different in driveability with either the vented gaskets or the solid gaskets on the end carbs; but that is conjecture, as all of my GTO's were 1964.
If I still had my 1964, I would convert it back to the single 4-barrel it had originally. I foolishly choose "eye candy" over performance when I converted from the single 4 to the tripower.
Jon.
__________________
"Good carburetion is fuelish hot air". 
"The most expensive carburetor is the wrong one given to you by your neighbor".
If you truly believe that "one size fits all" try walking a mile in your spouse's shoes!
Owner of The Carburetor Shop, LLC (of Missouri).
Current caretaker of the remains of Stromberg Caburetor, and custodian of the existing Carter and Kingston carburetor drawings.
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