It's a an significant difference considering you could just increase the stock evga clock speed to match ftw without adding any voltage (safe overclock). The frames difference can vary but it will be 1-2 frames on demanding games
Looking only at the first game it goes from 51.6FPS to 54.9. This is an increase of ~6%. Different games will show different percent. I'm guessing 6-8% will be the common difference.