Is the EM5’s Miss-Stated ISO concerning to you?

Funny thing, Pentax (K10D, K20D) used to have 1 stop darker images than older Olympus DSLRs, back when Olympus used Kodak then Panasonic  sensors, they often tested with higher ISO's than what their numbers said.  I think the old Panasonic used Sony sensors.

Now, Olympus moved to the Sony sensor and their true ISO versus claimed has dropped.  Back when Olympus ISO's were higher, you could claim that noise issues were less than the APS people claimed about 4/3rds cameras because of the higher tested ISO. The main problem with an ISO that is 1 stop lower than claimed is that your lens prices (f/2.8 versus f/4.0) to maintain the same image illumination and noise characteristics have to double to keep up.