X series ISO Inflation

Agreed. I remember taking both the E-M5 and the X-Pro1 to the Natural History Museum in London, which was dimly lit. The results from the E-M5 were noisier but (generally) sharper (partly down to IBIS countering hand shake at low shutter speeds). That said, if you ignore the stated ISO setting only and look at the output there is an advantage to the X-Pro1 and it IS a wee bit better in low light than my old NEX-5N too.

The results from both cameras cleaned in LR, with the E-M5 needing a little more noise reduction (but not orders of magnitude different). However, with the noise reduction applied (even if the same amount was applied) you see the differences in the sensors through the attractiveness of the output and (this is anecdotal, but in my opinion) the E-M5 output is slightly less attractive in such circumstances. I generally convert such (heavily NR) output to B&W and add synthetic grain to make it more acceptable (take away noise to add in grain  ).

However, that shouldn't surprise anyone even if the only difference between the two was in sensor size.

--
http://sgoldswoblog.wordpress.com
http://www.flickr.com/photos/sgoldswo/