Unless there is some problem with materials of construction, my assessment is that a Coriolis meter would be the best choice. The Coriolis meter is the only true mass flow meter and has the greatest accuracy and rangeability of any flow measurement. I don't know of any viscosity limitations. The temperatures and pressures cited are within the specs of the meter. If the accumulation of solids is a concern in the U-tube or bend of the highest performance Coriolis meter designs, a straight tube Coriolis meter can be used but the accuracy and rangeability is less.