I would say if your photography domain is ISO 200 or less with the Sigma's for when you need the better quality shots, there's really no reason (imho) for you to get the RX1 unless some operational issue was really getting in the way of the photos you wanted to take.
I don't have a DP2M only because I do shoot in available light/low light but if I was shooting in daylight and low ISO, I would have bought one yesterday
Just commenting, I get the impression you know exactly what you want, don't mean to sound like I know any better.
- Raist