I did give another listen on a good receiver... With the compressor off a little more lows/bass in the audio and leans more toward a good clean sound, much like were used to listening on the bands..
The compressor tightens up the audio a bit.. More of a cut-thru-the-mustard sound. They both sound good though and have their place.
I noticed that by cranking the Mod pot up it dropped the alc level on the meter and seem to give the Icom a bit more "headroom" before she would buck the alc.. kinda hard to explain, but it works better all the way around with the mod Pot cranked wide open and the Mic gain at 4% with compressor on, and about 15% with compressor off, you might get away with 20% but at that point I detect a 'bit of distortion, something that may or may not be heard out in radio land.
Just my .02 cents... And that ain't worth much in this day and age!!
'73's,
Kevin