A quick search throws up this for testing and this and this for statements? Though in each case the "the Enmity Widget on FFXIV-APP" is quoted.
Overpower is generally taken to be 120 Potency at a 5x multiplier for 600 Potency total.
SC is 200 Potency, if it's a 3x multipler then with Unchained up to cancel out Defiance; it should effectively equal Overpower at 600 potency... but if it's a 5x multiplier then doing that should hit 1000 potency.
A quick way to check would be to have two equally geared WARs: War #1 uses Steel Cyclone, War #2 uses Unchained + Overpower + Heavy Swing. Assuming no crits, that's a little over 700 raw potency total from War #2 (there'll be an extra bit of enmity generated from the extra two ability activations) versus either 600 or 1000 from War #1... so depending on who has hate at the end, there's your answer.
I can probably badger my brother into testing this with me on Monday night after Coil if nobody's bothered to do it before then.