I pretty much run single 4 barrel carbs, but the only time that I ever noticed issues that were corrected but jet extensions, were on the launch. If you have a stumble in high gear, I would be looking at fuel delivery issues. Back in the 70s, I was racing my 66 Fairlane 390 GTA, and it started to lay down in high gear, turned out the gas was uncovering the pickup tube of the stock gas tank, when the tank was much below 1/2 tank. Added a couple of gallons of gas, and it was cured. To check to see if jet extension may help, try raising the primary float levels and see if that helps. I did that on my Fairmont when I first installed a transbrake many years ago, the harder launch caused a stumble on the launch, raising the rear float 3/4 of a turn cured it, but you have to be careful that the higher float level doesn`t cause other issues, like dumping fuel into the boosters at idle, or downtrack further.