OMD versus G5, IQ

Hello

I already saw comparisons and debates concerning Panasonic and Olympus "larger" m4/3, but I ended up getting confused.

Concerning specifications, i can read or find out.

But I am not sure about Image Quality. I understand OMD IQ is better than G5. But WHY? (apart from lenses, where I read that the zoom usually put in a kit with the OMD is not very good... true?). But with the same lens? What makes OMD have a better IQ than G5? (or G3)

Thank-you in advance

--
Roberto