Zowie mice use the 3310 sensor, which is an earlier generation of the 3360 sensor in the G502. From a technical perspective, it should feel roughly the same on the Xim4, once you adjust the sensitivity (multiply your G502 sensitivity values by 3.75 for the Zowie).
Where you'll feel a difference is the grip. You'll either prefer the EC-2A or the G502. Simple as that.
Personally, I prefer the G303 over the Zowie FK2, mostly because of the slightly smaller size of the G303, which is better suited to my fingertip grip. Logitech mice also feel better constructed - the Zowie scrollwheel in particular feels flimsy.
Upgrade to the latest Xim4 firmware to ensure the Zowie mousewheel works.