Okay, well, consider the test complete.
I had a level 4 marza shoot down pirate defense turrets. Here are the times it took for the marza to kill its turret.
Control (no abilities)-- 1:07
Radiation Bomb Lvl 1-- 58
Incendiary Shelss Lvl 1-- 1:04
Radiation Bomb Lvl 2-- 53
Incendiary Shells Lvl 2-- 1:02
As you can see, the Rad bomb did far more damage to the target. It also did significantly more damage to the surrounding turrets than a Marza that isn't focusing its fire (and btw, by default, all the Marza's weapons focus on a single target...)
In other words, Rad Bomb is better.
On another note, I also discovered the Marza to be the only ship in the game capable of taking out an entire pirate base by itself. Thanks to the pirates' lack of shields/mitigation, the Marza can kill them all in one round of Missile Barrage.