Has anyone compared the pictures on dpreview.com under "16. Noise & Noise Reduction" for the OM-D EM-5? http://www.dpreview.com/reviews/olympusem5/16
Compare the OM-D with a Panasonic DMC-G3, Sony NEX-7 and a Samsung NX200. Look at the tests for both JPEG and RAW. This is a little hard to do since NEX-7 only has noise reduction "High Low or Normal" and no apparent OFF. With NR "off" the Samsung is the cleanest up thru 6400, but the image produced by the Samsung is almost invisible at this stage. I guess great ISO is possible but if the picture is hard to see, why bother? Of the 4, the OM-D and NEX-7 are very close at NR=Low setting.
In the ACR Raw noise test (lets face it, RAW is where you see what the sensor can really do, internal processing can only degrade the image SOMEWHERE) the OM-D is far better up to 3200 with ACR NR off, not only are the test swatches smoother, the image is clearer. Again, the Samsung has better swatch but the image is too washed out to be useful.
I think DxO does a real service with their test results and they are useful for comparison before a purchase but primarily, I need to consider the results of the picture as I see it as the final factor.
I bought an OM-D in July and the results have been everything I hoped for. Great shots at incredibly slow speeds (11x14 is beautiful with 1/15 sec hand-held shots of a stream). Very clean shots up to 1600 (what ISO is that really? who knows but in evening light and with no flash I get great shots, that's what counts). Kind of reminds me of when I ditched my Brownie and bought my first Nikon.