DSLR Check has published a ISO noise comparison test between Olympus E-PL5 vs Sony NEX-5R. As you can see here, there isn’t much difference to really nick pick. If you look at ISO6400 and ISO12800, I’m not sure if the NEX-5R with its larger sensor captures any more details. If anything, I can see certain details better in the E-PL5 images! This is interesting given that both uses Sony sensors and E-PL5 sensor is smaller.
Check out the full resolution image at the source link.