Difference in Sound Between Klipsch Cornwall IV & earlier generations of Cornwalls ?

The size of the cabinet is the same, but the ports are different and the horn that most of the music comes from is much larger, which has to make for a big difference.

Big difference mainly due to the updated midrange horn and far better tweeters. That said you can update the older ones with excellent results. I'd recommend looking at Bob Crites web site they have just about cornered the market on upgrades to older Klipsch speakers.   I did some Older laScalas a few years ago and they were hugely better after updates. Do some research and decide if that's a less expensive path for you to follow.  Also of note there used ones of the current version popping up now for much less.

If you were close to Victoria BC Canada I know of a 2022 used set coming out of an estate sale with about 3 months of use. The gentleman who owned them unfortunately passed just a few months after he received them. They are black ash, no box's so local Victoria / Vancouver / Seattle area pick up only.