It is also worth trying ISO640 at EV-2 and push in Post-Processing, much like using the M8 in Raw mode. Results probably vary by individual camera and shooting habits. This has to do with analog pre-amp settings vs 14-bits of digital range. I would use a smaller card, I like 8GByte 4x Sandisk. Use a fully charged battery. Post the results, I will try next time shooting limited light.