Idle feed restrictions are somewhat of a compromise on Holleys, as I've found out. Manufacture recommendations of 1/2 - 1 1/2 turns on the idle screws are pretty good to follow. I use both idle sound and vacuum to set mine. Ideally you want to have an air fuel ratio of 15 or 16:1 at idle and low load (cruising). At full throttle, full load, ignition advance all in, you want about 12:1 for max performance without pinging, or surging. That O2 sensor is actually better for finding your WOT jetting than anything else. I have had some luck canibalizing several carbs of different sizes to get a combo that works good throughout the range. I have about 20 parts carbs laying around my shop. This requires a lot of time patience and a good idea of where, in the power curve, your mixture needs improvement. Use your O2 sensor to get the WOT jetting right and adjust bleed screws by vacuum gauge and ear.