Ive done this mod. Its not on a gsxs/gsx-f, but I am using the GSXR brembo calipers.
I did see where someone did the math on this.Their figures were related to how much extra power you would get from changing a 300mm set of rotors to a 310mm . I forget the precise figure, but it was somewhere between 3 and 3.5%. Not very much, based only on rotor size, only.
For sure, you want to do a brake pad upgrade, before rotors. If you have weak pads, just that size change wont do much. Second step should be to upgrade your master cylinder. That Brembo rcs 19 would work really well with our Brembo calipers.
One interesting thing I did notice was in testing a set of 310mm Galfer wave rotors as compared to my 310mm brembo rotors. If you really want that huge hit, just as you grab the lever, the Galfer wave rotor will give you that. For me, I liked the more progressive and smooth feel from the round, Brembo rotor.