Bottom line, rent each system and try it side-by-side.
Long answer, I shoot the GX7 and D800 side-by-side, but during my travels, the D800 is increasing become a boat-anchor because of size and weight. I use the 7-14 and the 14-140 and with a pocket of batteries (the weak point of the system), and it is liberating!
Normal master image for me is 14x19 and the GX7 is fine. 30x40 with good craft and good technique is easy but I think pushing it, especially if you are like me and view the print from 18-24 inches. 3-4 feet away, its fine.
For travel, I'm getting older and the Nikons are heavier and bulkier. The GX7 is getting me better than my previous Nikon bodies, the D700/D300, especially in low light. I'd say that the GX7 is at least as good as the D700 and much better than the D300 by a stop or so at ISO 3200. The D800 still gets me better IQ but for all practical purposes, convenience and liberation vs. ultimate image quality is the bottom line.
The Sony is a good system, has a good set of lenses and one can adapt many other lenses to it, but then you are back to the size/weight issues that your present camera gives you.
Yes, there's ultimate IQ and noise issues with the M43 system, it lags behind current DSLR systems by a few years, but it's totally viable. The images will look different much like the images from my Hasselblad had a different look from my Nikon and large format. Not good, not bad. Different.
If you want the best pixels, stay with what you have. If you want liberation from sticking out, weight, size, impact to your joints from packing heavy iron, go with the m43 and learn to see again.