Take a look at this thread by djozz, he was able to get well over 4 amps into a well sinked XP-G2. That was a few years ago though and I don’t know if XP-G2s are suffering from the same ailment XM-L2s seem exhibiting (not handling as much amperage as they used to).
I have a couple of lights with XP-G2s, 1 at 3.8A the other at 4.2A, no problem with either one.