I've looked at lots of examples and I believe the M5 has an edge in sharpness, resolution and contrast. Noise seems about the same. I like the M1 body, but they did something to the camera that changed the image look from the M5. The difference is small, but it reminded me a lot of the image differences between Nikon's D800 and D800E. It is almost like a slight veil is lifted from the lens. I have not compared the M1 and M5 directly, only gone off the review site's comparisons, however.
When the E-M1 was issued, i thought very hard about it : i wanted the 12-40mm and there was an appreciable rebate when getting the kit. I went to an Olympus demo back in october, but found that while some buttons were nicely placed for my hands, not all where. The backwheel was a little to high for my hands (the same reason why i'm not using the horizontal grip on the E-M5) and lastly, i appreciate the smaller form factor of the E-M5. The VF was superb however and very tempting. So it was a hard decision, but in the end i stayed with the E-M5.
Later when the DXO results appeared, i was a little surprised, but the E-M5 seems to have an edge, or their evaluation have changed, or the on sensor PDAF comes at a price.. Or this is due to the new much faster processing engine ?
One sure problem is that when using the E-M1 without long exposure noise reduction (aka without dark frame subtraction) it is much more noisy than the E-M5 : a real problem for astro photography. This was clearly demonstrated by different photographers on the DPReview forum.
So in the end, while i regreat the new VF4 like finder, i'm happy with my decision. All the more so that i don't need PDAF. However, unless you need long exposure without darkframe substraction, in usual shooting conditions, there is no clear difference between the two cameras.
PS : It is curious, i just checked the DXO results and now the E-M1 is getting slightly better results than the E-M5, save for noise :
http://www.dxomark.com/Cameras/Compare/Side-by-side/Olympus-OM-D-E-M1-versus-Olympus-OM-D-E-M5___909_793
I remember that people were having issues with the GX7 results and in the comment section at the time i wondered about the compared results of the E-M1 and E-M5.. May be that they checked their results again.. I didn't follow up at the time.
Those difference are minimal, but when you look at the lenses results, they do systematically show somewhat less resolution than when put on the E-M5 sensor although i didn't check it right now).