I agree with Marshall, that any shock of modern build is lightyears better than stock.
The K75S has a YSS-MZ366, and I really don't notice it much, which is a great thing! It did take a long time to dial in, as there's a broad range for the spring and damping clicks (165lbs mostly 1-up riding). It adjusts for 2-up fairly fast, and a Sharpie mark on the threads get's it close enough to ride. A new shock will be a fantastic $200-300 upgrade.
* If I was to buy again, it'd be for the slightly shorter version, not the OEM length.