ISO Question

Hiya guys, quick question, ive got a shoot on sat with the BMC MFT camera. It will be a bright sunny day so I will be shooting with my ND in. I am going to have a shutter angle of 180 not 90 as there will be people in the frame and I don't want it to look like saving private ryan. So if its really bright out doors I just want to know, if I shoot 200 ISO instead of 400 or 800, will that effect anything apart from the speed. I was on a shoot the other week on a Red and I was told that the lower the ISO the less Dynamic Range, is this true as when I heard that I wasn't 100% sure.

you will loose about 1 to 1,5 stops of dynamic range. when shooting RAW it is anyway only metadata.