Turbo reduces the delay enough so that you will do that much more damage.
10% turbo = 10/11(90.9%) reload time, resulting in 10% more damage
25% turbo = 80% reload time, resulting in 25% more damage
40% turbo = 5/7(71.4%) reload time, resulting in 40% more damage
50% turbo = 2/3(66.6%) reload time, resulting in 50% more damage
60% turbo = 5/8(62.5%) reload time, resulting in 60% more damage
80% turbo = 5/9(55.5%)) reload time, resulting in 80% more damage
100% turbo = 50% reload time, resulting in 100% more damage
Turbo currenlty stacks additively using the highest 'Turbo Weapons (Equip)', 'Turbo Beam/ML/PL (Equip)', and the last applied 'Turbo Weapons (Activated)'. Unless there is a hidden cap, values higher than 100% would work the same, 200% turbo would be 1/3 reload time, resulting in 200% more damage.