Let's say that 4 survivors are all working on the same gen with purple toolboxes with the best add-ons (not including brand new part) and all of the best perks to complete the generator as fast as possible. How fast would that generator be completed?
Edit: Here's what I could find to help
4 survivors working on a gen takes a base of 28.57 seconds
A purple toolbox increases repair speed by 25% (There is no listing for the add-ons)
Prove Thy Self increases work speed by 10% for all survivors near by (This perk can't stack so it would only be 10% for each survivor)
Resilience increases repair speed by 9% while injured
Spine Chill increases repair speed by 6% while the killer is looking at you
Edit 2: All of the speed increases combined would give a 200% speed increase but with all 4 survivors working on the same gen you get around a 30% speed decrease Giving you a 170% increase to working speed