modulation is pretty much a function of set up. The rotors make little differenc. Where the G2 and G3 rotors improve over the Roundagons is less heat build up and quicker heat disipation. Also due to better slotting they keep the caliper clear of mud a guck better. And they're a tad lighter as well. Other than that a BB7 or BB5 have the same potential for power and modulation with a Roundagon as with a G2 or G3 rotor.
I have BB7s and went from a roundagon to a G2. Modulation was unchanged. The G2 seemed to require less effort. I couldn't get either rotor to fade after many attempts so I can't comment on fade resistance but from my own tests posted on here a long time ago the G2 seemed to run cooler. Noise was reduced with the G2 especially when wet.