First, there are two pressures applied to the rubber diaphragm, one is the ambient air pressure provided via the half moon crescent on the mouth of the carb and the other is the hole which allows the vacuum in the throat of the carb to be applied above the rubber diaphragm.
If one opens the throttle there will an increase in vacuum above the diaphragm transferred from the throat through the hole which eventually will overcome the tension of the spring and the slide opens which allows more air and fuel to enter.
So, the diameter of the hole will regulate how quickly the slide opens and closes. Notice, we are talking about fractions of second here.
Drilling the slide is not a way of gaining horsepower, but is more fine tuning.
Be very careful when you're dealing with the slides as the diaphram will tear if you're not careful and they are around $100 each!
Apparently, a larger hole has caused poor drivability issues, if you muck up or the larger hole mucks up the drivability, you can't put the material back.
Slide flutter is just one problem with a throttle slide hole that is too large. Another is that the slide can rise too quickly and cause a hesitation.
Just do NOT Drill your slides! There is nothing to Gain!
If you really want to drill holes...just buy you a drill bit (under 1/8th ) for a dollar instead of paying $99 for a Kit that just has a drill bit included.