There is of course DPR and they do RAW comparisons as well.
From ImagingResource :
JPG o/p
ISO200
EP3 -
http://www.imaging-resource.com/PRODS/EP3/FULLRES/EP3hSLI00200NR2D.HTM
NEX5n -
http://www.imaging-resource.com/PRODS/NEX5N/FULLRES/NEX5NhSLI00200_NR_STD_D.HTM
The NEX does have ISO100 over the base ISO200 of EP3.
But at ISO200, it does seem pretty comparable with EP3 with a bit of the upper hand.
However the NEX is a 16mp file and should really be down sampled to a 12mp file like the EP3 (or EP3 up scaled to match NEX).
ISO800
EP3 -
http://www.imaging-resource.com/PRODS/EP3/FULLRES/EP3hSLI00800NR2D.HTM
NEX5n -
http://www.imaging-resource.com/PRODS/NEX5N/FULLRES/NEX5NhSLI00800_NR_STD_D.HTM
NEX starts to pull away in detail, even with the larger file.
ISO1600
EP3 -
http://www.imaging-resource.com/PRODS/EP3/FULLRES/EP3hSLI01600NR2D.HTM
NEX5n -
http://www.imaging-resource.com/PRODS/NEX5N/FULLRES/NEX5NhSLI01600_NR_STD_D.HTM
By ISO1600, the colored cloths are very much smeared on the EP3 samples.
The NEX retains very good detail.
Those interested can explore more sample shots on the IR comparometer :
http://www.imaging-resource.com/IMCOMP/COMPS01.HTM
Does it mean anything on prints, or viewing?
>> All depends on print and viewing size.
I certainly don't print A3, A2, A1 regularly. Perhaps twice a year.
On such sizes, viewing distance is further, and prints I made with my 6mp DSLR has been as satisfactory as a picture on the wall as the one by a 14mp and 16mp camera.
I certainly don't have a TV monitor that can display a photo at 4036x2036 (It would be the size of a wall??).
So in many cases, large amounts of MP don't matter much.
But when I press the 1:1 button and see the difference, of course a bit 'bua song'
Does it mean
current APS-C is better?
>> Yes, for detail retention at higher ISO.
I like the oly colors more though (one of the few reasons I did not get a NEX). But that is tweakable with slight magenta bias in WB or PP.
Does it mean APS-C camera is better?
>> Certainly not.
The best camera is the one the photographer has when he/she needs it.
The best camera is the one that he knows how best to work with (warts and all)
Whether ISO800 or 1600 is important or not. Depends on the individual.
Eg. For many events (esp. weddings) its a difference between keeping the ambient (while the subject is lit with flash) or just having a flash lit shot.
Indoors, ISO800 and 1600 is common enough, both with and w/o flash.
Some folks shoot mostly studio; outdoors in good light; with a tripod.
To them high iso is not relevant in most cases.
Good photos can come from any camera. The camera is just a tool.
A painter can paint using a '01' ; '00'. '000' brush or opt for an air brush.
He may even just splash paint with a bucket onto the canvas.
The camera is just like the brush, air-brush, or bucket, just a tool the photographer chooses as he/she sees fit.
The photographer/artist is the one that makes the picture.
In not too challenging indoor lighting, for the same FOV, my GF1 can shoot at f1.7 with a 35mm DOF equivalent to f3.4.
Better DOF to resist focus error due to slight shifts in the subjects.
A FF camera shooting in the same condition at f1.7 would have very shallow DOF, and is easily OOF with the slightest shifting of the subject or even photographer swaying.
If the FF camera stops down to f3.4 to get the same DOF, it needs to increase ISO accordingly.
So the lines are never too clear in many cases.