That would be really interesting.. but i'm not in position to test as I don't have both cameras..
If we could get both camera to use the same lens, shoot at same target in the same low light environment with same aperture.
1) Test 1: Both camera select same shutter speed.
Compare brightness of picture, the one with higher exposure has higher sensitivity.
2) Test 2: Let camera choose it's own shutter speed.
If one camera chooses a higher shutter speed - that camera has higher sensitivity. But the difficult part is making sure brightness of both picture is exactly the same. And this part is really subjective and debatable.
I have no intention of supporting any brand... just that I don't know the answer to this.
In fact I'm currently looking at DSLR to replace the GF1.