I have CCU to one in buy back. I think the Ares Ion will probably be able to one-shot a light/medium fighter if they can get it targeted from long range, but will depend on how far it can target. I like the idea of being a ship 'sniper', but if you miss and get caught by a anything smaller than a Cutlass/Freelancer sized ship, I think you will most likely get FUBAR'd from there agility and not being able to bring that massive gun on them. But then again, it might be pretty nimble... Who knows
Either of them are going to bring the pain on slow/static, or larger targets though.