FYI Kath can't give stress if using the ion cannon. Ion cannon cancels all dice results if successful.
But opportunist and gunner seems like a decent combo. I used it in a 2 YT list once. I have since replaced it with different upgrades to make the 2 YT list more of a tank vs more damage output.
Actually this is incorrect. You roll your attack dice and modify said dice. Crits that result then need to be defended. Any hits/crits that are not defended are then negated, the defender receives 1 ion token and 1 damage.
So you can indeed stress a target and give him an ion token.
You are wrong. RTFM. I've cut and pasted directly from the FAQ below. Page 7, middle of the right column. Kath CAN NOT give stress when using an ion cannon.