Kaz, as long as you keep Auto ISO limited to 1600, you should be fine - and that's enough for a lot of situations. My OM-D E-M5 III uses the same sensor as your E-M1 II - and it's a solid one. You can even get away with ISO 3200 for most things - I often shoot high contrast in darker conditions and don't like too much noise in uniform dark surfaces, hence the 1600 limit. I used to cap older 12MP sensors at ISO 800 and keep ISO as low as possible - but this 20MP sensor is much better, and much more forgiving.
M.