When you mentioned you had the idle screw all way in, it tells me something is not adjusted right hence compensating by increasing rpm with a semi-open throttle. The initial setting of 1 turn out from slightly seated is just that "initial" because it ensures proper lube and minimum amount of fuel to start the engine. But for the motor to continue to idle, the idle screw must be set at least to 900-1000 in neutral on muffs.
I have exactly the same engine and yes, it sure idles more smoothly at less than 1 turn out on the idle mixture screw. The reason is obvious, there is better ratio of fuel-oil mix and air thus better combustion. In fact, in this setting, there is also less smoke from the exhaust. HOWEVER, there is also less oil going into the cylinders those reduced lubrication which can seriously damaged an engine.
If you still believe your hearing is a better tool for tuning up your motor, obviously you can do so. Personally, I go with the service manual or from experience which I believe is referred to a Good Engineering Practices. One piston replacement will set you back at least $250 if you do the job yourself or more than $700 if done by a certified mechanic.