If you would rule out the GM1 due to handling issues, I'd make sure you take a good long hard look at the RX100 before buying IT too. Some people love it, as you've seen. I personally found it to be an amazingly capable little camera with handling that I hated - never got used to it, learned to like it, adapted to it, etc.. We still have it in the family - I gave it to my wife who uses cameras very differently than I do - and every time I pick it up I'm reminded of how much I didn't bond with it, basically because of handling / interface issues. Many of which stem from it being so small... If you've used one a lot and KNOW you like it, that's another thing. But if you're just assuming you'd like the RX100 but are pretty sure you don't like the GM1, I'd take a second look at your assumptions.
The RX100 / RX10 sensor is good enough as an ONLY for a lot of folks or as a second / backup for others. But I'd think twice about dumping m43 for it. The newer m43 sensors are just better and to the extent it's a close call, the faster lenses put the nail in that coffin. Comparing the RX100 to most of the m43 kit zooms, though, is a pretty tough call and the RX100 becomes a lot more compelling. But compared to the faster m43 lenses, not all that close a call IMHO...
-Ray