Regarding the OP question, now that I have more games in with IG, I would favor C over D. It might have to do with my personal playstyle, but I boost a lot with the IGs, either before a k-turn/S-Loop thanks to advanced Sensor, or just to get back faster into the fight and realign my arc. So, the free Evade would help me a lot to survive even longer, especially since I don't run them with PtL, so the free action is nice. With Predator, it gets even more nastier: Boost, Evade and mini TL.
As for D, the hard k-turn is nice, for sure, but when I tried it, I didn't get as much milage as I thought I would. I did it just because I could, not because it was the best move to do. I can already do a hard k-turn by boosting prior to a S-Loop, and it also cover more distance, something that you want to get with the cannons and Autothrusters.
So, for my playstyle, The boost action is the action I do the most with IG just after focus. If I were to run a dual IG build, I would definetly go for B and C. But since I run only one, I go for B. That second attack chance is just pure gold. I just got a full health Corran out of the game tonight thanks to B gunner ability and a Ion Cannon; priceless. No other ship could have done it: Shoot a stress Corran with Ion cannon-AdvSensor bank Boost before k-turn to get behind him-gunner him with Ion Cannon-AdvS focus behind him and continue to Ion him until he's dead.