The 16-35 will give you a shutter speed that is twice as fast (e.g. 1/16 instead of 1/8), if you shoot it at f/2.8. But that may or may not mean that you have to use a tripod depending on the circumstances. If you need f/4 to get the DOF deep enough, for example, then it would not. The 17-55 f/2.8 IS would allow you to hand-hold slower shutter speeds if there is no movement in the frame.