I wouldn't worry at all about the ISO. The 5D3 has almost the same DR value up through ISO 800 (1/2 stop difference between 100 and 800), so as long as you stay under 800, you are fine. If you have to pull shadows up, there is more than enough DR there for that. The 5D3 doesn't have much noise at all at these levels too, and are very EASILY cleaned up if there are some. At this point I would be more concerned with AF, points, AF setup, shutter speed, and DOF/aperture, as you continue to learn. Those have a much larger impact on your results at this point.
Were these with center point and then recomposed, or were outer points used?