Lumix GX1 compared to my old LX3
Along with 2 friends, I had a chance to try shot-for-shot comparisons between an LX3, my LX5, an EP1 and a GF2 at a wedding, shot on an overcast damp day with most of the shots indoors. We also swapped cameras to even out any differences between our abilities...
Like you I had expected the two m4/3 cameras to do far better than the LX3/5, however this was not the case and I was surprised by the results.
On the LX3 and LX5 we were shooting handheld at f/2, 1/8 sec and ISO200, pretty much the limit. Sometimes adding some soft fill flash, by bouncing the light off a card to the ceiling.
For the m4/3 caneras, any advantage from a larger sensor was basically negated by the slower kit lenses they were using - 2 stops slower meant they had to start at ISO800 or 1600, or have blurred shots.
After 700 shots between us, the resulting photo album is comprised of 45% shots from the LX5, 35% from the LX3, and a handful from the other two.
To be fair, if the m4/3 cameras had fast lenses like the new 12-35 f/2.8 from Panasonic, or the 20mm f/1.7 it would have been a much more interesting comparison, and they would have done a lot better.