This is not a weapon test so numbers are irrelevant - all that matters is difference in damage done per one unit of measurement between same class fixed, gimbaled and turret variant.
For thermic weapons unit of measurement always is one full WEP capacitor charge, for multi-cannons one clip and for cannons one shot or one clip (depending on damage done, because sometimes one shot does less than 1%), but what matters is how much better one variant is compared to another against exactly same taarget and by using same unit of measurement.
|Gimbaled vs Turret||5-7%||9-11%|
|Fixed vs Turret||24%||25-34%|
|Fixed vs Gimbaled||18-19%||15-28%|
|Gimbaled vs Turret||41-42%||28-43%|
|Fixed vs Turret||51-57%||50-60%|
|Fixed vs Gimbaled||17-25%||30%|
As you can see thermic weapon variants lose less compared to kinetic. I would even say that kinetic turrets are not useful at all - while gimbaled variants deal around 20-30% less damage kinetic turrets are 50-60% weaker than fixed weapons.
For thermic weapons (lasers) turrets actually might be very wise choice because they can track enemies in a much wider arc than gimbaled and they are only slightly weaker than - around 10%. But keep in mind that higher the class turret you have slower it will track target and miss many shots - even while I was testing Large Cannon and Pulse Laser turrets they missed shots at non moving target from 500 meters away and that target was Anaconda, so not really a small ship.
Most useful turrets would be small or medium class thermic weapons on large ships, because they wont eat much of your power plant, wont require that much of your WEP capacitor charge and can track effectively small enemies.