Macro doesn't seem to be the RX100's strong suit. If you really want to concentrate on macro, there might be a better option out there.
Early generation Rx100s were slightly better at macro. Rx100 versions I and II had zoom lenses that went to 37mn (100mm in 35mm camera terms) whereas subsequent models only went to 26mm (70mm equivalent). It's the telephoto capability that provides the magnification, generally, and the diopter provides the ability to focus closely (at the expense of being able to focus far). Obviously, being able to focus closer let's you get the camera closer and therefore make the subject larger, so both the zoomed focal length and the diopter affect macro performance, but diopters aren't camera-dependent. So, any camera can get close enough to use the telephoto capability the camera has, but it's the telephoto capability (or lack thereof) that's the real differentiator in effective magnification and working distance. Shorter innate close focus ability on the long end of the zoom range let's you use weaker diopters, with potentially less adverse effect on image quality.
Being able to zoom to 100mm instead of 70mm does help, but it's not an enormous bump. Moreover, later models have better glass in the sense of general image quality across the available zoom range, the lens is also brighter (doesn't help macro, but it helps otherwise), the later sensors have better low light performance and dynamic range, they're faster (both in frames per second and general responsiveness), have better video, and (what is to me *huuugely* important) later models have Auto ISO minimum shutter speed function. That's a lot to give up for slightly better macro, IMO.
Getting 1:1 on an Rx100 probably won't be easy. I don't know exactly, but you'll probably need something like a +10 diopter (difficult to use, but you've got a huge dive count, so maybe not for you), and a subject willing to let you really get in its face. 1:2 and crop from there seems more achievable for us mortals. Fortunately, Sony makes great sensors.
