Are you sure you are looking at the MkII ?
The MkI DR is lower in extended low at Bill's site, but the PDR for the MkII remains much the same. This appears to have changed since I last looked at it about 12 months ago. Or I am going dippier than I thought I was? Always a strong possibility!
http://photonstophotos.net/Charts/PDR.htm#Olympus%20OM-D%20E-M1,Olympus%20OM-D%20E-M1%20Mark%20II
Got to post this. My tablet had to be rebooted because it spat the dummy!