I don't know that they are any harder to hold steady, but high X's sure amplify the effect your movements. That can often cause folks to try harder to keep steady and adversely affect the rest of the shooting equation. When I first went from the big bull to a 5-spot target in archery league I was introduced to "target panic", and I believe the same holds true for increased magnification and handguns. It's all mental, y'know?