Depends on games really mostly but Let's say between Stock and FTW you will get like ~9% increase in fps
So that is the max increase from the lowest to the highest
The SC to Stock I would say even though nothing official but you will be talking about ~3% increase in fps
SSC is around ~6% from stock
All of the fps increase I am talking about is at 1080p it is lower at higher resolutions of course
But if you get the ACX 2.0 Cooled non superclocked and you want to overclock it yourself depending on the luck of the draw you might have the same overclock speed that you get from the FTW so it's mostly about you if you want to overclock yourself or go with the already overclocked versions
Hope that what you needed here