I have a 3.5" camo cynergy. Have been using heavily for ducks since 2014 or so. 26". Fits me well, have gotten more 25s in skeet with it than any other gun also. I hunt in a , layout boat, a wide kayak, and I never have any issues reloading gun fast.
I have a 20ga 725, but no other Citori. However, as others say, the receiver on cynergy is slimmer and not as tall--perfect for me, but I can see there might be a height difference on fit between the two.
I personally like the cynergy for waterfowl better, due to: good camo, strong action with very little unexposed polished metal so easy to clean and wipe dry. Adjustable comb!! To me, shooting from a blind while sitting makes a huge mount difference from standing with maybe a slight forward lean! So being able to tweak comb height is huge. Excellent recoil pad with deep rubber absorbing area-- this is the older cynergy with the wierd looking curved recoil pad cut, but it is much better at absorbing heavy 3" loads if needed.
Lastly, great triggers. I don't know various citori triggers, but cynergy with mechanical NEVER let me down, even if I use 3/4oz or light tss duplex loads.