I just did some quick and dirty with the LX7 because I was planning to return it today but wanted to check the raws first. First impression is pretty similar to jpegs. Very useable up to 800, marginal in the 1000-1250 range, and pretty bad by 1600. Lots of noise even at 400 and 800, but still looks good after using Lightroom NR. 1600 has so much noise (in low to medium light) that any detail is already pretty much blown to pieces and NR just smooths out the lack of detail, but its not a choice between detail and noise - the detail was shot. The RX100 jpegs are already sooo much better and it can't be any worse with raw, so I don't even need to check those out right away - I'll just be shooting raw+jpeg for awhile until I see whether there's a compelling reason to go one way or the other and then I'll go that direction. I'd say the LX7 is about a stop better than the LX5 though, maybe slightly more - I was never happy with the LX5 above 400, so there's definitely improvement in that sensor - just not enough to compete with the Sony.
I was stil sort of conflicted about sending the LX7 back because I find it so much more fun to shoot with and I was thinking, 'well, my compact doesn't really NEED to be good in low light - I've got an OMD and X-Pro for that'. But then I did some back to back tests with the GRD3 and its not notably different - both are very workable to 800 and the exposure values aren't too different at the same focal length and approximately the same aperture (f1.8 vs f1.9). And the place where the LX7 is way more useable than the RX100 is for street shooting, but its no more fun than the GRD! So, the LX7 is going back and the RX100 and GRD3 are staying so I'll have both a really fun street camera and a really good IQ compact for more general shooting. Bottom line - I don't really have to think about the RX100's limits when I grab it to take along somewhere - it'll handle damn near anything within its focal range. The LX7 I'd have to really think about and wouldn't take it a lot of times I would take the RX100... Not a tough call really, as much as I like the direction of the LX7...
-Ray